| # | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
|---|
| Punctuation | |
|---|---|
| . | Execute commands from a file in the current shell. |
| : | Null command. |
| [ | Execute conditional command. |
| [[ | Execute conditional command. |
| { | Group commands as a unit. |
| A | |
| alias | Define or display aliases. |
| arch | Print machine hardware name. |
| B | |
| base64 | Base64 encode/decode data. |
| basename | Strip directory and suffix. |
| bg | Move jobs to the background. |
| bind | Set Readline key bindings and variables. |
| break | Exit for, while, or until loops. |
| builtin | Execute shell builtins. |
| C | |
| caller | Return the context of the current subroutine call. |
| case | Execute commands based on pattern matching. |
| cat | Concatenate and write files. |
| cd | Change the shell working directory. |
| chcon | Change SELinux CTX of files. |
| chgrp | Change file groups. |
| chmod | Change access permissions. |
| chown | Change file owners and groups. |
| chroot | Specify the root directory. |
| cksum | Print POSIX CRC checksum. |
| comm | Compare sorted files by line. |
| command | Execute a simple command or display information about commands. |
| compgen | Display possible completions depending on the options. |
| complete | Specify how arguments are to be completed by Readline. |
| compopt | Modify or display completion options. |
| continue | Resume for, while, or until loops. |
| coproc | Create a coprocess named NAME. |
| coreutils | Multi-call program. |
| cp | Copy files. |
| csplit | Split by context. |
| cut | Print selected parts of lines. |
| D | |
| date | Print/set system date and time. |
| dd | Copy and convert a file. |
| declare | Set variable values and attributes. |
| df | Report file system disk usage. |
| dir | List directories briefly. |
| dircolors | Color setup for ls. |
| dirname | Strip last file name component. |
| dirs | Display directory stack. |
| disown | Remove jobs from current shell. |
| du | Report on disk usage. |
| E | |
| echo | Print a line of text. |
| echo | Print a line of text. |
| enable | Enable and disable shell builtins. |
| env | Modify the environment. |
| eval | Execute arguments as a shell command. |
| exec | Replace the shell with the given command. |
| exit | Exit the shell. |
| expand | Convert tabs to spaces. |
| export | Set export attribute for shell variables. |
| expr | Evaluate expressions. |
| F | |
| factor | Print prime factors |
| false | Do nothing, unsuccessfully. |
| false | Do nothing, unsuccessfully. |
| fc | Display or execute commands from the history list. |
| fg | Move job to the foreground. |
| fmt | Reformat paragraph text. |
| fold | Wrap long input lines. |
| for | Execute commands for each member in a list. |
| function | Define shell function. |
| G | |
| getopts | Parse option arguments. |
| groups | Print group names a user is in. |
| H | |
| hash | Remember or display program locations. |
| head | Output the first part of files. |
| help | Display information about builtin commands. |
| history | Display or manipulate the history list. |
| hostid | Print numeric host identifier. |
| hostname | Print or set system name. |
| I | |
| id | Print user identity. |
| if | Execute commands based on conditional. |
| install | Copy files and set attributes. |
| J | |
| jobs | Display status of jobs. |
| join | Join lines on a common field. |
| K | |
| kill | Send a signal to processes. |
| kill | Send a signal to processes. |
| L | |
| let | Evaluate arithmetic expressions. |
| link | Make hard links between files. |
| ln | Make links between files. |
| local | Define local variables. |
| logname | Print current login name. |
| logout | Exit a login shell. |
| ls | List directory contents. |
| M | |
| mapfile | Read lines from the standard input into an indexed array variable. |
| md5sum | Print or check MD5 digests. |
| mkdir | Create directories. |
| mkfifo | Create FIFOs (named pipes). |
| mknod | Create special files. |
| mktemp | Create temporary files. |
| mv | Rename files. |
| N | |
| nice | Modify niceness. |
| nl | Number lines and write files. |
| nohup | Immunize to hangups. |
| nproc | Print the number of processors. |
| numfmt | Reformat numbers. |
| O | |
| od | Dump files in octal, etc. |
| P | |
| paste | Merge lines of files. |
| pathchk | Check file name portability. |
| popd | Remove directories from stack. |
| pr | Paginate or columnate files. |
| printenv | Print environment variables. |
| printf | Format and print data. |
| printf | Format and print data. |
| ptx | Produce permuted indexes. |
| pushd | Add directories to stack. |
| pwd | Print working directory. |
| pwd | Print working directory. |
| R | |
| read | Read a line from the standard input and split it into fields. |
| readarray | Read lines from a file into an array variable. |
| readlink | Print referent of a symlink. |
| readonly | Mark shell variables as unchangeable. |
| realpath | Print resolved file names. |
| return | Return from a shell function. |
| rm | Remove files. |
| rmdir | Remove empty directories. |
| runcon | Run in specified SELinux CTX. |
| S | |
| select | Select words from a list and execute commands. |
| seq | Print numeric sequences |
| set | Set or unset values of shell options and positional parameters. |
| sha1sum | Print or check SHA-1 digests. |
| sha2 | Print or check SHA-2 digests. |
| shift | Shift positional parameters. |
| shopt | Set and unset shell options. |
| shred | Remove files more securely. |
| shuf | Shuffling text files. |
| sleep | Delay for a specified time. |
| sort | Sort text files. |
| source | Execute commands from a file in the current shell. |
| split | Split into pieces. |
| stat | Report file(system) status. |
| stdbuf | Modify stdio buffering. |
| stty | Print/change terminal settings. |
| sum | Print traditional checksum. |
| suspend | Suspend shell execution. |
| sync | Synchronize memory and disk. |
| T | |
| tac | Reverse files. |
| tail | Output the last part of files. |
| tee | Redirect to multiple files. |
| test | File/string tests. |
| test | File/string tests. |
| time | Report time consumed by pipeline's execution. |
| timeout | Run with time limit. |
| times | Display process times. |
| touch | Change file timestamps. |
| tr | Translate characters. |
| trap | Trap signals and other events. |
| true | Do nothing, successfully. |
| true | Do nothing, successfully. |
| truncate | Shrink/extend size of a file. |
| tsort | Topological sort. |
| tty | Print terminal name. |
| type | Display information about command type. |
| typeset | Set variable values and attributes. |
| U | |
| ulimit | Modify shell resource limits. |
| umask | Display or set file mode mask. |
| unalias | Remove each NAME from the list of defined aliases. |
| uname | Print system information. |
| unexpand | Convert spaces to tabs. |
| uniq | Uniquify files. |
| unlink | Removal via unlink(2). |
| unset | Unset values and attributes of shell variables and functions. |
| until | Execute commands as long as a test does not succeed. |
| uptime | Print uptime and load. |
| users | Print current user names. |
| V | |
| vdir | List directories verbosely. |
| W | |
| wait | Wait for job completion and return exit status. |
| wc | Line, word, and byte counts. |
| while | Execute commands as long as a test succeeds. |
| who | Print who is logged in. |
| whoami | Print effective user ID. |
| Y | |
| yes | Print a string indefinitely. |
(builtin command)
.: . filename [arguments]
Execute commands from a file in the current shell.
Read and execute commands from FILENAME in the current shell. The
entries in $PATH are used to find the directory containing FILENAME.
If any ARGUMENTS are supplied, they become the positional parameters
when FILENAME is executed.
Exit Status:
Returns the status of the last command executed in FILENAME; fails if
FILENAME cannot be read.
(builtin command)
:: :
Null command.
No effect; the command does nothing.
Exit Status:
Always succeeds.
(builtin command)
[[ ... ]]: [[ expression ]]
Execute conditional command.
Returns a status of 0 or 1 depending on the evaluation of the conditional
expression EXPRESSION. Expressions are composed of the same primaries used
by the 'test' builtin, and may be combined using the following operators:
( EXPRESSION ) Returns the value of EXPRESSION
! EXPRESSION True if EXPRESSION is false; else false
EXPR1 && EXPR2 True if both EXPR1 and EXPR2 are true; else false
EXPR1 || EXPR2 True if either EXPR1 or EXPR2 is true; else false
When the '==' and '!=' operators are used, the string to the right of
the operator is used as a pattern and pattern matching is performed.
When the '=~' operator is used, the string to the right of the operator
is matched as a regular expression.
The && and || operators do not evaluate EXPR2 if EXPR1 is sufficient to
determine the expression's value.
Exit Status:
0 or 1 depending on value of EXPRESSION.
(reserved word)
[[ ... ]]: [[ expression ]]
Execute conditional command.
Returns a status of 0 or 1 depending on the evaluation of the conditional
expression EXPRESSION. Expressions are composed of the same primaries used
by the 'test' builtin, and may be combined using the following operators:
( EXPRESSION ) Returns the value of EXPRESSION
! EXPRESSION True if EXPRESSION is false; else false
EXPR1 && EXPR2 True if both EXPR1 and EXPR2 are true; else false
EXPR1 || EXPR2 True if either EXPR1 or EXPR2 is true; else false
When the '==' and '!=' operators are used, the string to the right of
the operator is used as a pattern and pattern matching is performed.
When the '=~' operator is used, the string to the right of the operator
is matched as a regular expression.
The && and || operators do not evaluate EXPR2 if EXPR1 is sufficient to
determine the expression's value.
Exit Status:
0 or 1 depending on value of EXPRESSION.
(reserved word)
{ ... }: { COMMANDS ; }
Group commands as a unit.
Run a set of commands in a group. This is one way to redirect an
entire set of commands.
Exit Status:
Returns the status of the last command executed.
(builtin command)
alias: alias [-p] [name[=value] ... ]
Define or display aliases.
Without arguments, 'alias' prints the list of aliases in the reusable
form 'alias NAME=VALUE' on standard output.
Otherwise, an alias is defined for each NAME whose VALUE is given.
A trailing space in VALUE causes the next word to be checked for
alias substitution when the alias is expanded.
Options:
-p Print all defined aliases in a reusable format
Exit Status:
alias returns true unless a NAME is supplied for which no alias has been
defined.
(coreutils)
'arch': Print machine hardware name
'arch' prints the machine hardware name, and is equivalent to 'uname
-m'. Synopsis:
arch [OPTION]
The program accepts the *note Common options:: only.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'base64': Transform data into printable data
'base64' transforms data read from a file, or standard input, into (or
from) base64 encoded form. The base64 encoded form uses printable ASCII
characters to represent binary data. Synopses:
base64 [OPTION]... [FILE]
base64 --decode [OPTION]... [FILE]
The base64 encoding expands data to roughly 133% of the original.
The format conforms to RFC 4648
(ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt).
The program accepts the following options. Also see *note Common
options::.
'-w COLS'
'--wrap=COLS'
During encoding, wrap lines after COLS characters. This must be a
positive number.
The default is to wrap after 76 characters. Use the value 0 to
disable line wrapping altogether.
'-d'
'--decode'
Change the mode of operation, from the default of encoding data, to
decoding data. Input is expected to be base64 encoded data, and
the output will be the original data.
'-i'
'--ignore-garbage'
When decoding, newlines are always accepted. During decoding,
ignore unrecognized bytes, to permit distorted data to be decoded.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'basename': Strip directory and suffix from a file name
'basename' removes any leading directory components from NAME.
Synopsis:
basename NAME [SUFFIX]
basename OPTION... NAME...
If SUFFIX is specified and is identical to the end of NAME, it is
removed from NAME as well. Note that since trailing slashes are removed
prior to suffix matching, SUFFIX will do nothing if it contains slashes.
'basename' prints the result on standard output.
Together, 'basename' and 'dirname' are designed such that if 'ls
"$name"' succeeds, then the command sequence 'cd "$(dirname "$name")";
ls "$(basename "$name")"' will, too. This works for everything except
file names containing a trailing newline.
POSIX allows the implementation to define the results if NAME is
empty or '//'. In the former case, GNU 'basename' returns the empty
string. In the latter case, the result is '//' on platforms where // is
distinct from /, and '/' on platforms where there is no difference.
The program accepts the following options. Also see *note Common
options::. Options must precede operands.
'-a'
'--multiple'
Support more than one argument. Treat every argument as a NAME.
With this, an optional SUFFIX must be specified using the '-s'
option.
'-s SUFFIX'
'--suffix=SUFFIX'
Remove a trailing SUFFIX. This option implies the '-a' option.
'-z'
'--zero'
Output a zero byte (ASCII NUL) at the end of each line, rather than
a newline. This option enables other programs to parse the output
even when that output would contain data with embedded newlines.
An exit status of zero indicates success, and a nonzero value
indicates failure.
Examples:
# Output "sort".
basename /usr/bin/sort
# Output "stdio".
basename include/stdio.h .h
# Output "stdio".
basename -s .h include/stdio.h
# Output "stdio" followed by "stdlib"
basename -a -s .h include/stdio.h include/stdlib.h
(builtin command)
bg: bg [job_spec ...]
Move jobs to the background.
Place the jobs identified by each JOB_SPEC in the background, as if they
had been started with '&'. If JOB_SPEC is not present, the shell's notion
of the current job is used.
Exit Status:
Returns success unless job control is not enabled or an error occurs.
(builtin command)
bind: bind [-lpsvPSVX] [-m keymap] [-f filename] [-q name] [-u name] [-r keyseq] [-x keyseq:shell-command] [keyseq:readline-function or readline-command]
Set Readline key bindings and variables.
Bind a key sequence to a Readline function or a macro, or set a
Readline variable. The non-option argument syntax is equivalent to
that found in ~/.inputrc, but must be passed as a single argument:
e.g., bind '"\C-x\C-r": re-read-init-file'.
Options:
-m keymap Use KEYMAP as the keymap for the duration of this
command. Acceptable keymap names are emacs,
emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move,
vi-command, and vi-insert.
-l List names of functions.
-P List function names and bindings.
-p List functions and bindings in a form that can be
reused as input.
-S List key sequences that invoke macros and their values
-s List key sequences that invoke macros and their values
in a form that can be reused as input.
-V List variable names and values
-v List variable names and values in a form that can
be reused as input.
-q function-name Query about which keys invoke the named function.
-u function-name Unbind all keys which are bound to the named function.
-r keyseq Remove the binding for KEYSEQ.
-f filename Read key bindings from FILENAME.
-x keyseq:shell-command Cause SHELL-COMMAND to be executed when
KEYSEQ is entered.
-X List key sequences bound with -x and associated commands
in a form that can be reused as input.
Exit Status:
bind returns 0 unless an unrecognized option is given or an error occurs.
(builtin command)
break: break [n]
Exit for, while, or until loops.
Exit a FOR, WHILE or UNTIL loop. If N is specified, break N enclosing
loops.
Exit Status:
The exit status is 0 unless N is not greater than or equal to 1.
(builtin command)
builtin: builtin [shell-builtin [arg ...]]
Execute shell builtins.
Execute SHELL-BUILTIN with arguments ARGs without performing command
lookup. This is useful when you wish to reimplement a shell builtin
as a shell function, but need to execute the builtin within the function.
Exit Status:
Returns the exit status of SHELL-BUILTIN, or false if SHELL-BUILTIN is
not a shell builtin..
(builtin command)
caller: caller [expr]
Return the context of the current subroutine call.
Without EXPR, returns "$line $filename". With EXPR, returns
"$line $subroutine $filename"; this extra information can be used to
provide a stack trace.
The value of EXPR indicates how many call frames to go back before the
current one; the top frame is frame 0.
Exit Status:
Returns 0 unless the shell is not executing a shell function or EXPR
is invalid.
(reserved word)
case: case WORD in [PATTERN [| PATTERN]...) COMMANDS ;;]... esac
Execute commands based on pattern matching.
Selectively execute COMMANDS based upon WORD matching PATTERN. The
'|' is used to separate multiple patterns.
Exit Status:
Returns the status of the last command executed.
(coreutils)
'cat': Concatenate and write files
'cat' copies each FILE ('-' means standard input), or standard input if
none are given, to standard output. Synopsis:
cat [OPTION] [FILE]...
The program accepts the following options. Also see *note Common
options::.
'-A'
'--show-all'
Equivalent to '-vET'.
'-b'
'--number-nonblank'
Number all nonempty output lines, starting with 1.
'-e'
Equivalent to '-vE'.
'-E'
'--show-ends'
Display a '$' after the end of each line.
'-n'
'--number'
Number all output lines, starting with 1. This option is ignored
if '-b' is in effect.
'-s'
'--squeeze-blank'
Suppress repeated adjacent empty lines; output just one empty line
instead of several.
'-t'
Equivalent to '-vT'.
'-T'
'--show-tabs'
Display TAB characters as '^I'.
'-u'
Ignored; for POSIX compatibility.
'-v'
'--show-nonprinting'
Display control characters except for LFD and TAB using '^'
notation and precede characters that have the high bit set with
'M-'.
On systems like MS-DOS that distinguish between text and binary
files, 'cat' normally reads and writes in binary mode. However, 'cat'
reads in text mode if one of the options '-bensAE' is used or if 'cat'
is reading from standard input and standard input is a terminal.
Similarly, 'cat' writes in text mode if one of the options '-bensAE' is
used or if standard output is a terminal.
An exit status of zero indicates success, and a nonzero value
indicates failure.
Examples:
# Output f's contents, then standard input, then g's contents.
cat f - g
# Copy standard input to standard output.
cat
(builtin command)
cd: cd [-L|[-P [-e]] [-@]] [dir]
Change the shell working directory.
Change the current directory to DIR. The default DIR is the value of the
HOME shell variable.
The variable CDPATH defines the search path for the directory containing
DIR. Alternative directory names in CDPATH are separated by a colon (:).
A null directory name is the same as the current directory. If DIR begins
with a slash (/), then CDPATH is not used.
If the directory is not found, and the shell option 'cdable_vars' is set,
the word is assumed to be a variable name. If that variable has a value,
its value is used for DIR.
Options:
-L force symbolic links to be followed: resolve symbolic links in
DIR after processing instances of '..'
-P use the physical directory structure without following symbolic
links: resolve symbolic links in DIR before processing instances
of '..'
-e if the -P option is supplied, and the current working directory
cannot be determined successfully, exit with a non-zero status
-@ on systems that support it, present a file with extended attributes
as a directory containing the file attributes
The default is to follow symbolic links, as if '-L' were specified.
'..' is processed by removing the immediately previous pathname component
back to a slash or the beginning of DIR.
Exit Status:
Returns 0 if the directory is changed, and if $PWD is set successfully when
-P is used; non-zero otherwise.
(coreutils)
'chcon': Change SELinux context of file
'chcon' changes the SELinux security context of the selected files.
Synopses:
chcon [OPTION]... CONTEXT FILE...
chcon [OPTION]... [-u USER] [-r ROLE] [-l RANGE] [-t TYPE] FILE...
chcon [OPTION]... --reference=RFILE FILE...
Change the SELinux security context of each FILE to CONTEXT. With
'--reference', change the security context of each FILE to that of
RFILE.
The program accepts the following options. Also see *note Common
options::.
'--dereference'
Do not affect symbolic links but what they refer to; this is the
default.
'-h'
'--no-dereference'
Affect the symbolic links themselves instead of any referenced
file.
'--reference=RFILE'
Use RFILE's security context rather than specifying a CONTEXT
value.
'-R'
'--recursive'
Operate on files and directories recursively.
'--preserve-root'
Refuse to operate recursively on the root directory, '/', when used
together with the '--recursive' option. *Note Treating /
specially::.
'--no-preserve-root'
Do not treat the root directory, '/', specially when operating
recursively; this is the default. *Note Treating / specially::.
'-H'
If '--recursive' ('-R') is specified and a command line argument is
a symbolic link to a directory, traverse it. *Note Traversing
symlinks::.
'-L'
In a recursive traversal, traverse every symbolic link to a
directory that is encountered. *Note Traversing symlinks::.
'-P'
Do not traverse any symbolic links. This is the default if none of
'-H', '-L', or '-P' is specified. *Note Traversing symlinks::.
'-v'
'--verbose'
Output a diagnostic for every file processed.
'-u USER'
'--user=USER'
Set user USER in the target security context.
'-r ROLE'
'--role=ROLE'
Set role ROLE in the target security context.
'-t TYPE'
'--type=TYPE'
Set type TYPE in the target security context.
'-l RANGE'
'--range=RANGE'
Set range RANGE in the target security context.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'chgrp': Change group ownership
'chgrp' changes the group ownership of each given FILE to GROUP (which
can be either a group name or a numeric group ID) or to the group of an
existing reference file. *Note chown invocation::. Synopsis:
chgrp [OPTION]... {GROUP | --reference=REF_FILE} FILE...
If GROUP is intended to represent a numeric group ID, then you may
specify it with a leading '+'. *Note Disambiguating names and IDs::.
It is system dependent whether a user can change the group to an
arbitrary one, or the more portable behavior of being restricted to
setting a group of which the user is a member.
The program accepts the following options. Also see *note Common
options::.
'-c'
'--changes'
Verbosely describe the action for each FILE whose group actually
changes.
'-f'
'--silent'
'--quiet'
Do not print error messages about files whose group cannot be
changed.
'--dereference'
Do not act on symbolic links themselves but rather on what they
point to. This is the default.
'-h'
'--no-dereference'
Act on symbolic links themselves instead of what they point to.
This mode relies on the 'lchown' system call. On systems that do
not provide the 'lchown' system call, 'chgrp' fails when a file
specified on the command line is a symbolic link. By default, no
diagnostic is issued for symbolic links encountered during a
recursive traversal, but see '--verbose'.
'--preserve-root'
Fail upon any attempt to recursively change the root directory,
'/'. Without '--recursive', this option has no effect. *Note
Treating / specially::.
'--no-preserve-root'
Cancel the effect of any preceding '--preserve-root' option. *Note
Treating / specially::.
'--reference=REF_FILE'
Change the group of each FILE to be the same as that of REF_FILE.
If REF_FILE is a symbolic link, do not use the group of the
symbolic link, but rather that of the file it refers to.
'-v'
'--verbose'
Output a diagnostic for every file processed. If a symbolic link
is encountered during a recursive traversal on a system without the
'lchown' system call, and '--no-dereference' is in effect, then
issue a diagnostic saying neither the symbolic link nor its
referent is being changed.
'-R'
'--recursive'
Recursively change the group ownership of directories and their
contents.
'-H'
If '--recursive' ('-R') is specified and a command line argument is
a symbolic link to a directory, traverse it. *Note Traversing
symlinks::.
'-L'
In a recursive traversal, traverse every symbolic link to a
directory that is encountered. *Note Traversing symlinks::.
'-P'
Do not traverse any symbolic links. This is the default if none of
'-H', '-L', or '-P' is specified. *Note Traversing symlinks::.
An exit status of zero indicates success, and a nonzero value
indicates failure.
Examples:
# Change the group of /u to "staff".
chgrp staff /u
# Change the group of /u and subfiles to "staff".
chgrp -hR staff /u
(coreutils)
'chmod': Change access permissions
'chmod' changes the access permissions of the named files. Synopsis:
chmod [OPTION]... {MODE | --reference=REF_FILE} FILE...
'chmod' never changes the permissions of symbolic links, since the
'chmod' system call cannot change their permissions. This is not a
problem since the permissions of symbolic links are never used.
However, for each symbolic link listed on the command line, 'chmod'
changes the permissions of the pointed-to file. In contrast, 'chmod'
ignores symbolic links encountered during recursive directory
traversals.
A successful use of 'chmod' clears the set-group-ID bit of a regular
file if the file's group ID does not match the user's effective group ID
or one of the user's supplementary group IDs, unless the user has
appropriate privileges. Additional restrictions may cause the
set-user-ID and set-group-ID bits of MODE or REF_FILE to be ignored.
This behavior depends on the policy and functionality of the underlying
'chmod' system call. When in doubt, check the underlying system
behavior.
If used, MODE specifies the new file mode bits. For details, see the
section on *note File permissions::. If you really want MODE to have a
leading '-', you should use '--' first, e.g., 'chmod -- -w file'.
Typically, though, 'chmod a-w file' is preferable, and 'chmod -w file'
(without the '--') complains if it behaves differently from what 'chmod
a-w file' would do.
The program accepts the following options. Also see *note Common
options::.
'-c'
'--changes'
Verbosely describe the action for each FILE whose permissions
actually changes.
'-f'
'--silent'
'--quiet'
Do not print error messages about files whose permissions cannot be
changed.
'--preserve-root'
Fail upon any attempt to recursively change the root directory,
'/'. Without '--recursive', this option has no effect. *Note
Treating / specially::.
'--no-preserve-root'
Cancel the effect of any preceding '--preserve-root' option. *Note
Treating / specially::.
'-v'
'--verbose'
Verbosely describe the action or non-action taken for every FILE.
'--reference=REF_FILE'
Change the mode of each FILE to be the same as that of REF_FILE.
*Note File permissions::. If REF_FILE is a symbolic link, do not
use the mode of the symbolic link, but rather that of the file it
refers to.
'-R'
'--recursive'
Recursively change permissions of directories and their contents.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'chown': Change file owner and group
'chown' changes the user and/or group ownership of each given FILE to
NEW-OWNER or to the user and group of an existing reference file.
Synopsis:
chown [OPTION]... {NEW-OWNER | --reference=REF_FILE} FILE...
If used, NEW-OWNER specifies the new owner and/or group as follows
(with no embedded white space):
[OWNER] [ : [GROUP] ]
Specifically:
OWNER
If only an OWNER (a user name or numeric user ID) is given, that
user is made the owner of each given file, and the files' group is
not changed.
OWNER':'GROUP
If the OWNER is followed by a colon and a GROUP (a group name or
numeric group ID), with no spaces between them, the group ownership
of the files is changed as well (to GROUP).
OWNER':'
If a colon but no group name follows OWNER, that user is made the
owner of the files and the group of the files is changed to OWNER's
login group.
':'GROUP
If the colon and following GROUP are given, but the owner is
omitted, only the group of the files is changed; in this case,
'chown' performs the same function as 'chgrp'.
':'
If only a colon is given, or if NEW-OWNER is empty, neither the
owner nor the group is changed.
If OWNER or GROUP is intended to represent a numeric user or group
ID, then you may specify it with a leading '+'. *Note Disambiguating
names and IDs::.
Some older scripts may still use '.' in place of the ':' separator.
POSIX 1003.1-2001 (*note Standards conformance::) does not require
support for that, but for backward compatibility GNU 'chown' supports
'.' so long as no ambiguity results. New scripts should avoid the use
of '.' because it is not portable, and because it has undesirable
results if the entire OWNER'.'GROUP happens to identify a user whose
name contains '.'.
It is system dependent whether a user can change the group to an
arbitrary one, or the more portable behavior of being restricted to
setting a group of which the user is a member.
The 'chown' command sometimes clears the set-user-ID or set-group-ID
permission bits. This behavior depends on the policy and functionality
of the underlying 'chown' system call, which may make system-dependent
file mode modifications outside the control of the 'chown' command. For
example, the 'chown' command might not affect those bits when invoked by
a user with appropriate privileges, or when the bits signify some
function other than executable permission (e.g., mandatory locking).
When in doubt, check the underlying system behavior.
The program accepts the following options. Also see *note Common
options::.
'-c'
'--changes'
Verbosely describe the action for each FILE whose ownership
actually changes.
'-f'
'--silent'
'--quiet'
Do not print error messages about files whose ownership cannot be
changed.
'--from=OLD-OWNER'
Change a FILE's ownership only if it has current attributes
specified by OLD-OWNER. OLD-OWNER has the same form as NEW-OWNER
described above. This option is useful primarily from a security
standpoint in that it narrows considerably the window of potential
abuse. For example, to reflect a user ID numbering change for one
user's files without an option like this, 'root' might run
find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
But that is dangerous because the interval between when the 'find'
tests the existing file's owner and when the 'chown' is actually
run may be quite large. One way to narrow the gap would be to
invoke chown for each file as it is found:
find / -owner OLDUSER -exec chown -h NEWUSER {} \;
But that is very slow if there are many affected files. With this
option, it is safer (the gap is narrower still) though still not
perfect:
chown -h -R --from=OLDUSER NEWUSER /
'--dereference'
Do not act on symbolic links themselves but rather on what they
point to. This is the default.
'-h'
'--no-dereference'
Act on symbolic links themselves instead of what they point to.
This mode relies on the 'lchown' system call. On systems that do
not provide the 'lchown' system call, 'chown' fails when a file
specified on the command line is a symbolic link. By default, no
diagnostic is issued for symbolic links encountered during a
recursive traversal, but see '--verbose'.
'--preserve-root'
Fail upon any attempt to recursively change the root directory,
'/'. Without '--recursive', this option has no effect. *Note
Treating / specially::.
'--no-preserve-root'
Cancel the effect of any preceding '--preserve-root' option. *Note
Treating / specially::.
'--reference=REF_FILE'
Change the user and group of each FILE to be the same as those of
REF_FILE. If REF_FILE is a symbolic link, do not use the user and
group of the symbolic link, but rather those of the file it refers
to.
'-v'
'--verbose'
Output a diagnostic for every file processed. If a symbolic link
is encountered during a recursive traversal on a system without the
'lchown' system call, and '--no-dereference' is in effect, then
issue a diagnostic saying neither the symbolic link nor its
referent is being changed.
'-R'
'--recursive'
Recursively change ownership of directories and their contents.
'-H'
If '--recursive' ('-R') is specified and a command line argument is
a symbolic link to a directory, traverse it. *Note Traversing
symlinks::.
'-L'
In a recursive traversal, traverse every symbolic link to a
directory that is encountered. *Note Traversing symlinks::.
'-P'
Do not traverse any symbolic links. This is the default if none of
'-H', '-L', or '-P' is specified. *Note Traversing symlinks::.
An exit status of zero indicates success, and a nonzero value
indicates failure.
Examples:
# Change the owner of /u to "root".
chown root /u
# Likewise, but also change its group to "staff".
chown root:staff /u
# Change the owner of /u and subfiles to "root".
chown -hR root /u
(coreutils)
'chroot': Run a command with a different root directory
'chroot' runs a command with a specified root directory. On many
systems, only the super-user can do this.(1) Synopses:
chroot OPTION NEWROOT [COMMAND [ARGS]...]
chroot OPTION
Ordinarily, file names are looked up starting at the root of the
directory structure, i.e., '/'. 'chroot' changes the root to the
directory NEWROOT (which must exist) and then runs COMMAND with optional
ARGS. If COMMAND is not specified, the default is the value of the
'SHELL' environment variable or '/bin/sh' if not set, invoked with the
'-i' option. COMMAND must not be a special built-in utility (*note
Special built-in utilities::).
The program accepts the following options. Also see *note Common
options::. Options must precede operands.
'--userspec=USER[:GROUP]'
By default, COMMAND is run with the same credentials as the
invoking process. Use this option to run it as a different USER
and/or with a different primary GROUP. If a USER is specified then
the supplementary groups are set according to the system defined
list for that user, unless overridden with the '--groups' option.
'--groups=GROUPS'
Use this option to override the supplementary GROUPS to be used by
the new process. The items in the list (names or numeric IDs) must
be separated by commas. Use '--groups=''' to disable the
supplementary group look-up implicit in the '--userspec' option.
The user and group name look-up performed by the '--userspec' and
'--groups' options, is done both outside and inside the chroot, with
successful look-ups inside the chroot taking precedence. If the
specified user or group items are intended to represent a numeric ID,
then a name to ID resolving step is avoided by specifying a leading '+'.
*Note Disambiguating names and IDs::.
Here are a few tips to help avoid common problems in using chroot.
To start with a simple example, make COMMAND refer to a statically
linked binary. If you were to use a dynamically linked executable, then
you'd have to arrange to have the shared libraries in the right place
under your new root directory.
For example, if you create a statically linked 'ls' executable, and
put it in '/tmp/empty', you can run this command as root:
$ chroot /tmp/empty /ls -Rl /
Then you'll see output like this:
/:
total 1023
-rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
If you want to use a dynamically linked executable, say 'bash', then
first run 'ldd bash' to see what shared objects it needs. Then, in
addition to copying the actual binary, also copy the listed files to the
required positions under your intended new root directory. Finally, if
the executable requires any other files (e.g., data, state, device
files), copy them into place, too.
Exit status:
125 if 'chroot' itself fails
126 if COMMAND is found but cannot be invoked
127 if COMMAND cannot be found
the exit status of COMMAND otherwise
---------- Footnotes ----------
(1) However, some systems (e.g., FreeBSD) can be configured to allow
certain regular users to use the 'chroot' system call, and hence to run
this program. Also, on Cygwin, anyone can run the 'chroot' command,
because the underlying function is non-privileged due to lack of support
in MS-Windows.
(coreutils)
'cksum': Print CRC checksum and byte counts
'cksum' computes a cyclic redundancy check (CRC) checksum for each given
FILE, or standard input if none are given or for a FILE of '-'.
Synopsis:
cksum [OPTION]... [FILE]...
'cksum' prints the CRC checksum for each file along with the number
of bytes in the file, and the file name unless no arguments were given.
'cksum' is typically used to ensure that files transferred by
unreliable means (e.g., netnews) have not been corrupted, by comparing
the 'cksum' output for the received files with the 'cksum' output for
the original files (typically given in the distribution).
The CRC algorithm is specified by the POSIX standard. It is not
compatible with the BSD or System V 'sum' algorithms (see the previous
section); it is more robust.
The only options are '--help' and '--version'. *Note Common
options::.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'comm': Compare two sorted files line by line
'comm' writes to standard output lines that are common, and lines that
are unique, to two input files; a file name of '-' means standard input.
Synopsis:
comm [OPTION]... FILE1 FILE2
Before 'comm' can be used, the input files must be sorted using the
collating sequence specified by the 'LC_COLLATE' locale. If an input
file ends in a non-newline character, a newline is silently appended.
The 'sort' command with no options always outputs a file that is
suitable input to 'comm'.
With no options, 'comm' produces three-column output. Column one
contains lines unique to FILE1, column two contains lines unique to
FILE2, and column three contains lines common to both files. Columns
are separated by a single TAB character.
The options '-1', '-2', and '-3' suppress printing of the
corresponding columns (and separators). Also see *note Common
options::.
Unlike some other comparison utilities, 'comm' has an exit status
that does not depend on the result of the comparison. Upon normal
completion 'comm' produces an exit code of zero. If there is an error
it exits with nonzero status.
If the '--check-order' option is given, unsorted inputs will cause a
fatal error message. If the option '--nocheck-order' is given, unsorted
inputs will never cause an error message. If neither of these options
is given, wrongly sorted inputs are diagnosed only if an input file is
found to contain unpairable lines. If an input file is diagnosed as
being unsorted, the 'comm' command will exit with a nonzero status (and
the output should not be used).
Forcing 'comm' to process wrongly sorted input files containing
unpairable lines by specifying '--nocheck-order' is not guaranteed to
produce any particular output. The output will probably not correspond
with whatever you hoped it would be.
'--check-order'
Fail with an error message if either input file is wrongly ordered.
'--nocheck-order'
Do not check that both input files are in sorted order.
Other options are:
'--output-delimiter=STR'
Print STR between adjacent output columns, rather than the default
of a single TAB character.
The delimiter STR may not be empty.
(builtin command)
command: command [-pVv] command [arg ...]
Execute a simple command or display information about commands.
Runs COMMAND with ARGS suppressing shell function lookup, or display
information about the specified COMMANDs. Can be used to invoke commands
on disk when a function with the same name exists.
Options:
-p use a default value for PATH that is guaranteed to find all of
the standard utilities
-v print a description of COMMAND similar to the 'type' builtin
-V print a more verbose description of each COMMAND
Exit Status:
Returns exit status of COMMAND, or failure if COMMAND is not found.
(builtin command)
compgen: compgen [-abcdefgjksuv] [-o option] [-A action] [-G globpat] [-W wordlist] [-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] [word]
Display possible completions depending on the options.
Intended to be used from within a shell function generating possible
completions. If the optional WORD argument is supplied, matches against
WORD are generated.
Exit Status:
Returns success unless an invalid option is supplied or an error occurs.
(builtin command)
complete: complete [-abcdefgjksuv] [-pr] [-DE] [-o option] [-A action] [-G globpat] [-W wordlist] [-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] [name ...]
Specify how arguments are to be completed by Readline.
For each NAME, specify how arguments are to be completed. If no options
are supplied, existing completion specifications are printed in a way that
allows them to be reused as input.
Options:
-p print existing completion specifications in a reusable format
-r remove a completion specification for each NAME, or, if no
NAMEs are supplied, all completion specifications
-D apply the completions and actions as the default for commands
without any specific completion defined
-E apply the completions and actions to "empty" commands --
completion attempted on a blank line
When completion is attempted, the actions are applied in the order the
uppercase-letter options are listed above. The -D option takes
precedence over -E.
Exit Status:
Returns success unless an invalid option is supplied or an error occurs.
(builtin command)
compopt: compopt [-o|+o option] [-DE] [name ...]
Modify or display completion options.
Modify the completion options for each NAME, or, if no NAMEs are supplied,
the completion currently being executed. If no OPTIONs are given, print
the completion options for each NAME or the current completion specification.
Options:
-o option Set completion option OPTION for each NAME
-D Change options for the "default" command completion
-E Change options for the "empty" command completion
Using '+o' instead of '-o' turns off the specified option.
Arguments:
Each NAME refers to a command for which a completion specification must
have previously been defined using the 'complete' builtin. If no NAMEs
are supplied, compopt must be called by a function currently generating
completions, and the options for that currently-executing completion
generator are modified.
Exit Status:
Returns success unless an invalid option is supplied or NAME does not
have a completion specification defined.
(builtin command)
continue: continue [n]
Resume for, while, or until loops.
Resumes the next iteration of the enclosing FOR, WHILE or UNTIL loop.
If N is specified, resumes the Nth enclosing loop.
Exit Status:
The exit status is 0 unless N is not greater than or equal to 1.
(reserved word)
coproc: coproc [NAME] command [redirections]
Create a coprocess named NAME.
Execute COMMAND asynchronously, with the standard output and standard
input of the command connected via a pipe to file descriptors assigned
to indices 0 and 1 of an array variable NAME in the executing shell.
The default NAME is "COPROC".
Exit Status:
Returns the exit status of COMMAND.
(coreutils)
'coreutils': Multi-call binary
'coreutils' invokes an individual utility, either implicitly selected by
the last component of 'argv[0]', or by explicitly calling 'coreutils'
with the '--coreutils-prog' option. Synopsis:
coreutils --coreutils-prog=PROGRAM ...
(coreutils)
'cp': Copy files and directories
'cp' copies files (or, optionally, directories). The copy is completely
independent of the original. You can either copy one file to another,
or copy arbitrarily many files to a destination directory. Synopses:
cp [OPTION]... [-T] SOURCE DEST
cp [OPTION]... SOURCE... DIRECTORY
cp [OPTION]... -t DIRECTORY SOURCE...
• If two file names are given, 'cp' copies the first file to the
second.
• If the '--target-directory' ('-t') option is given, or failing that
if the last file is a directory and the '--no-target-directory'
('-T') option is not given, 'cp' copies each SOURCE file to the
specified directory, using the SOURCEs' names.
Generally, files are written just as they are read. For exceptions,
see the '--sparse' option below.
By default, 'cp' does not copy directories. However, the '-R', '-a',
and '-r' options cause 'cp' to copy recursively by descending into
source directories and copying files to corresponding destination
directories.
When copying from a symbolic link, 'cp' normally follows the link
only when not copying recursively or when '--link' ('-l') is used. This
default can be overridden with the '--archive' ('-a'), '-d',
'--dereference' ('-L'), '--no-dereference' ('-P'), and '-H' options. If
more than one of these options is specified, the last one silently
overrides the others.
When copying to a symbolic link, 'cp' follows the link only when it
refers to an existing regular file. However, when copying to a dangling
symbolic link, 'cp' refuses by default, and fails with a diagnostic,
since the operation is inherently dangerous. This behavior is contrary
to historical practice and to POSIX. Set 'POSIXLY_CORRECT' to make 'cp'
attempt to create the target of a dangling destination symlink, in spite
of the possible risk. Also, when an option like '--backup' or '--link'
acts to rename or remove the destination before copying, 'cp' renames or
removes the symbolic link rather than the file it points to.
By default, 'cp' copies the contents of special files only when not
copying recursively. This default can be overridden with the
'--copy-contents' option.
'cp' generally refuses to copy a file onto itself, with the following
exception: if '--force --backup' is specified with SOURCE and DEST
identical, and referring to a regular file, 'cp' will make a backup
file, either regular or numbered, as specified in the usual ways (*note
Backup options::). This is useful when you simply want to make a backup
of an existing file before changing it.
The program accepts the following options. Also see *note Common
options::.
'-a'
'--archive'
Preserve as much as possible of the structure and attributes of the
original files in the copy (but do not attempt to preserve internal
directory structure; i.e., 'ls -U' may list the entries in a copied
directory in a different order). Try to preserve SELinux security
context and extended attributes (xattr), but ignore any failure to
do that and print no corresponding diagnostic. Equivalent to '-dR
--preserve=all' with the reduced diagnostics.
'--attributes-only'
Copy only the specified attributes of the source file to the
destination. If the destination already exists, do not alter its
contents. See the '--preserve' option for controlling which
attributes to copy.
'-b'
'--backup[=METHOD]'
*Note Backup options::. Make a backup of each file that would
otherwise be overwritten or removed. As a special case, 'cp' makes
a backup of SOURCE when the force and backup options are given and
SOURCE and DEST are the same name for an existing, regular file.
One useful application of this combination of options is this tiny
Bourne shell script:
#!/bin/sh
# Usage: backup FILE...
# Create a GNU-style backup of each listed FILE.
fail=0
for i; do
cp --backup --force --preserve=all -- "$i" "$i" || fail=1
done
exit $fail
'--copy-contents'
If copying recursively, copy the contents of any special files
(e.g., FIFOs and device files) as if they were regular files. This
means trying to read the data in each source file and writing it to
the destination. It is usually a mistake to use this option, as it
normally has undesirable effects on special files like FIFOs and
the ones typically found in the '/dev' directory. In most cases,
'cp -R --copy-contents' will hang indefinitely trying to read from
FIFOs and special files like '/dev/console', and it will fill up
your destination disk if you use it to copy '/dev/zero'. This
option has no effect unless copying recursively, and it does not
affect the copying of symbolic links.
'-d'
Copy symbolic links as symbolic links rather than copying the files
that they point to, and preserve hard links between source files in
the copies. Equivalent to '--no-dereference --preserve=links'.
'-f'
'--force'
When copying without this option and an existing destination file
cannot be opened for writing, the copy fails. However, with
'--force', when a destination file cannot be opened, 'cp' then
removes it and tries to open it again. Contrast this behavior with
that enabled by '--link' and '--symbolic-link', whereby the
destination file is never opened but rather is removed
unconditionally. Also see the description of
'--remove-destination'.
This option is independent of the '--interactive' or '-i' option:
neither cancels the effect of the other.
This option is ignored when the '--no-clobber' or '-n' option is
also used.
'-H'
If a command line argument specifies a symbolic link, then copy the
file it points to rather than the symbolic link itself. However,
copy (preserving its nature) any symbolic link that is encountered
via recursive traversal.
'-i'
'--interactive'
When copying a file other than a directory, prompt whether to
overwrite an existing destination file. The '-i' option overrides
a previous '-n' option.
'-l'
'--link'
Make hard links instead of copies of non-directories.
'-L'
'--dereference'
Follow symbolic links when copying from them. With this option,
'cp' cannot create a symbolic link. For example, a symlink (to
regular file) in the source tree will be copied to a regular file
in the destination tree.
'-n'
'--no-clobber'
Do not overwrite an existing file. The '-n' option overrides a
previous '-i' option. This option is mutually exclusive with '-b'
or '--backup' option.
'-P'
'--no-dereference'
Copy symbolic links as symbolic links rather than copying the files
that they point to. This option affects only symbolic links in the
source; symbolic links in the destination are always followed if
possible.
'-p'
'--preserve[=ATTRIBUTE_LIST]'
Preserve the specified attributes of the original files. If
specified, the ATTRIBUTE_LIST must be a comma-separated list of one
or more of the following strings:
'mode'
Preserve the file mode bits and access control lists.
'ownership'
Preserve the owner and group. On most modern systems, only
users with appropriate privileges may change the owner of a
file, and ordinary users may preserve the group ownership of a
file only if they happen to be a member of the desired group.
'timestamps'
Preserve the times of last access and last modification, when
possible. On older systems, it is not possible to preserve
these attributes when the affected file is a symbolic link.
However, many systems now provide the 'utimensat' function,
which makes it possible even for symbolic links.
'links'
Preserve in the destination files any links between
corresponding source files. Note that with '-L' or '-H', this
option can convert symbolic links to hard links. For example,
$ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
74161745 a
74161745 b
Note the inputs: 'b' is a symlink to regular file 'a', yet the
files in destination directory, 'c/', are hard-linked. Since
'-a' implies '--no-dereference' it would copy the symlink, but
the later '-H' tells 'cp' to dereference the command line
arguments where it then sees two files with the same inode
number. Then the '--preserve=links' option also implied by
'-a' will preserve the perceived hard link.
Here is a similar example that exercises 'cp''s '-L' option:
$ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
74163295 a
74163295 b
'context'
Preserve SELinux security context of the file, or fail with
full diagnostics.
'xattr'
Preserve extended attributes of the file, or fail with full
diagnostics. If 'cp' is built without xattr support, ignore
this option. If SELinux context, ACLs or Capabilities are
implemented using xattrs, they are preserved implicitly by
this option as well, i.e., even without specifying
'--preserve=mode' or '--preserve=context'.
'all'
Preserve all file attributes. Equivalent to specifying all of
the above, but with the difference that failure to preserve
SELinux security context or extended attributes does not
change 'cp''s exit status. In contrast to '-a', all but
'Operation not supported' warnings are output.
Using '--preserve' with no ATTRIBUTE_LIST is equivalent to
'--preserve=mode,ownership,timestamps'.
In the absence of this option, the permissions of existing
destination files are unchanged, while each new file is created
with the mode bits of the corresponding source file, minus the bits
set in the umask and minus the set-user-ID and set-group-ID bits.
*Note File permissions::.
'--no-preserve=ATTRIBUTE_LIST'
Do not preserve the specified attributes. The ATTRIBUTE_LIST has
the same form as for '--preserve'.
'--parents'
Form the name of each destination file by appending to the target
directory a slash and the specified name of the source file. The
last argument given to 'cp' must be the name of an existing
directory. For example, the command:
cp --parents a/b/c existing_dir
copies the file 'a/b/c' to 'existing_dir/a/b/c', creating any
missing intermediate directories.
'-R'
'-r'
'--recursive'
Copy directories recursively. By default, do not follow symbolic
links in the source unless used together with the '--link' ('-l')
option; see the '--archive' ('-a'), '-d', '--dereference' ('-L'),
'--no-dereference' ('-P'), and '-H' options. Special files are
copied by creating a destination file of the same type as the
source; see the '--copy-contents' option. It is not portable to
use '-r' to copy symbolic links or special files. On some non-GNU
systems, '-r' implies the equivalent of '-L' and '--copy-contents'
for historical reasons. Also, it is not portable to use '-R' to
copy symbolic links unless you also specify '-P', as POSIX allows
implementations that dereference symbolic links by default.
'--reflink[=WHEN]'
Perform a lightweight, copy-on-write (COW) copy, if supported by
the file system. Once it has succeeded, beware that the source and
destination files share the same disk data blocks as long as they
remain unmodified. Thus, if a disk I/O error affects data blocks
of one of the files, the other suffers the same fate.
The WHEN value can be one of the following:
'always'
The default behavior: if the copy-on-write operation is not
supported then report the failure for each file and exit with
a failure status.
'auto'
If the copy-on-write operation is not supported then fall back
to the standard copy behaviour.
This option is overridden by the '--link', '--symbolic-link' and
'--attributes-only' options, thus allowing it to be used to
configure the default data copying behavior for 'cp'. For example,
with the following alias, 'cp' will use the minimum amount of space
supported by the file system.
alias cp='cp --reflink=auto --sparse=always'
'--remove-destination'
Remove each existing destination file before attempting to open it
(contrast with '-f' above).
'--sparse=WHEN'
A "sparse file" contains "holes": a sequence of zero bytes that does
not occupy any physical disk blocks; the 'read' system call reads
these as zeros. This can both save considerable disk space and
increase speed, since many binary files contain lots of consecutive
zero bytes. By default, 'cp' detects holes in input source files
via a crude heuristic and makes the corresponding output file
sparse as well. Only regular files may be sparse.
The WHEN value can be one of the following:
'auto'
The default behavior: if the input file is sparse, attempt to
make the output file sparse, too. However, if an output file
exists but refers to a non-regular file, then do not attempt
to make it sparse.
'always'
For each sufficiently long sequence of zero bytes in the input
file, attempt to create a corresponding hole in the output
file, even if the input file does not appear to be sparse.
This is useful when the input file resides on a file system
that does not support sparse files (for example, 'efs' file
systems in SGI IRIX 5.3 and earlier), but the output file is
on a type of file system that does support them. Holes may be
created only in regular files, so if the destination file is
of some other type, 'cp' does not even try to make it sparse.
'never'
Never make the output file sparse. This is useful in creating
a file for use with the 'mkswap' command, since such a file
must not have any holes.
'--strip-trailing-slashes'
Remove any trailing slashes from each SOURCE argument. *Note
Trailing slashes::.
'-s'
'--symbolic-link'
Make symbolic links instead of copies of non-directories. All
source file names must be absolute (starting with '/') unless the
destination files are in the current directory. This option merely
results in an error message on systems that do not support symbolic
links.
'-S SUFFIX'
'--suffix=SUFFIX'
Append SUFFIX to each backup file made with '-b'. *Note Backup
options::.
'-t DIRECTORY'
'--target-directory=DIRECTORY'
Specify the destination DIRECTORY. *Note Target directory::.
'-T'
'--no-target-directory'
Do not treat the last operand specially when it is a directory or a
symbolic link to a directory. *Note Target directory::.
'-u'
'--update'
Do not copy a non-directory that has an existing destination with
the same or newer modification time. If time stamps are being
preserved, the comparison is to the source time stamp truncated to
the resolutions of the destination file system and of the system
calls used to update time stamps; this avoids duplicate work if
several 'cp -pu' commands are executed with the same source and
destination. If '--preserve=links' is also specified (like with
'cp -au' for example), that will take precedence. Consequently,
depending on the order that files are processed from the source,
newer files in the destination may be replaced, to mirror hard
links in the source.
'-v'
'--verbose'
Print the name of each file before copying it.
'-x'
'--one-file-system'
Skip subdirectories that are on different file systems from the one
that the copy started on. However, mount point directories _are_
copied.
'-Z'
'--context[=CONTEXT]'
Without a specified CONTEXT, adjust the SELinux security context
according to the system default type for destination files,
similarly to the 'restorecon' command. The long form of this
option with a specific context specified, will set the context for
newly created files only. With a specified context, if both
SELinux and SMACK are disabled, a warning is issued. This option
is mutually exclusive with the '--preserve=context' option, and
overrides the '--preserve=all' and '-a' options.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'csplit': Split a file into context-determined pieces
'csplit' creates zero or more output files containing sections of INPUT
(standard input if INPUT is '-'). Synopsis:
csplit [OPTION]... INPUT PATTERN...
The contents of the output files are determined by the PATTERN
arguments, as detailed below. An error occurs if a PATTERN argument
refers to a nonexistent line of the input file (e.g., if no remaining
line matches a given regular expression). After every PATTERN has been
matched, any remaining input is copied into one last output file.
By default, 'csplit' prints the number of bytes written to each
output file after it has been created.
The types of pattern arguments are:
'N'
Create an output file containing the input up to but not including
line N (a positive integer). If followed by a repeat count, also
create an output file containing the next N lines of the input file
once for each repeat.
'/REGEXP/[OFFSET]'
Create an output file containing the current line up to (but not
including) the next line of the input file that contains a match
for REGEXP. The optional OFFSET is an integer. If it is given,
the input up to (but not including) the matching line plus or minus
OFFSET is put into the output file, and the line after that begins
the next section of input.
'%REGEXP%[OFFSET]'
Like the previous type, except that it does not create an output
file, so that section of the input file is effectively ignored.
'{REPEAT-COUNT}'
Repeat the previous pattern REPEAT-COUNT additional times. The
REPEAT-COUNT can either be a positive integer or an asterisk,
meaning repeat as many times as necessary until the input is
exhausted.
The output files' names consist of a prefix ('xx' by default)
followed by a suffix. By default, the suffix is an ascending sequence
of two-digit decimal numbers from '00' to '99'. In any case,
concatenating the output files in sorted order by file name produces the
original input file.
By default, if 'csplit' encounters an error or receives a hangup,
interrupt, quit, or terminate signal, it removes any output files that
it has created so far before it exits.
The program accepts the following options. Also see *note Common
options::.
'-f PREFIX'
'--prefix=PREFIX'
Use PREFIX as the output file name prefix.
'-b SUFFIX'
'--suffix=SUFFIX'
Use SUFFIX as the output file name suffix. When this option is
specified, the suffix string must include exactly one
'printf(3)'-style conversion specification, possibly including
format specification flags, a field width, a precision
specifications, or all of these kinds of modifiers. The format
letter must convert a binary unsigned integer argument to readable
form. The format letters 'd' and 'i' are aliases for 'u', and the
'u', 'o', 'x', and 'X' conversions are allowed. The entire SUFFIX
is given (with the current output file number) to 'sprintf(3)' to
form the file name suffixes for each of the individual output files
in turn. If this option is used, the '--digits' option is ignored.
'-n DIGITS'
'--digits=DIGITS'
Use output file names containing numbers that are DIGITS digits
long instead of the default 2.
'-k'
'--keep-files'
Do not remove output files when errors are encountered.
'--suppress-matched'
Do not output lines matching the specified PATTERN. I.E. suppress
the boundary line from the start of the second and subsequent
splits.
'-z'
'--elide-empty-files'
Suppress the generation of zero-length output files. (In cases
where the section delimiters of the input file are supposed to mark
the first lines of each of the sections, the first output file will
generally be a zero-length file unless you use this option.) The
output file sequence numbers always run consecutively starting from
0, even when this option is specified.
'-s'
'-q'
'--silent'
'--quiet'
Do not print counts of output file sizes.
An exit status of zero indicates success, and a nonzero value
indicates failure.
Here is an example of its usage. First, create an empty directory
for the exercise, and cd into it:
$ mkdir d && cd d
Now, split the sequence of 1..14 on lines that end with 0 or 5:
$ seq 14 | csplit - '/[05]$/' '{*}'
8
10
15
Each number printed above is the size of an output file that csplit
has just created. List the names of those output files:
$ ls
xx00 xx01 xx02
Use 'head' to show their contents:
$ head xx*
==> xx00 <==
1
2
3
4
==> xx01 <==
5
6
7
8
9
==> xx02 <==
10
11
12
13
14
Example of splitting input by empty lines:
$ csplit --suppress-matched INPUT.TXT '/^$/' '{*}'
(coreutils)
'cut': Print selected parts of lines
'cut' writes to standard output selected parts of each line of each
input file, or standard input if no files are given or for a file name
of '-'. Synopsis:
cut OPTION... [FILE]...
In the table which follows, the BYTE-LIST, CHARACTER-LIST, and
FIELD-LIST are one or more numbers or ranges (two numbers separated by a
dash) separated by commas. Bytes, characters, and fields are numbered
starting at 1. Incomplete ranges may be given: '-M' means '1-M'; 'N-'
means 'N' through end of line or last field. The list elements can be
repeated, can overlap, and can be specified in any order; but the
selected input is written in the same order that it is read, and is
written exactly once.
The program accepts the following options. Also see *note Common
options::.
'-b BYTE-LIST'
'--bytes=BYTE-LIST'
Select for printing only the bytes in positions listed in
BYTE-LIST. Tabs and backspaces are treated like any other
character; they take up 1 byte. If an output delimiter is
specified, (see the description of '--output-delimiter'), then
output that string between ranges of selected bytes.
'-c CHARACTER-LIST'
'--characters=CHARACTER-LIST'
Select for printing only the characters in positions listed in
CHARACTER-LIST. The same as '-b' for now, but internationalization
will change that. Tabs and backspaces are treated like any other
character; they take up 1 character. If an output delimiter is
specified, (see the description of '--output-delimiter'), then
output that string between ranges of selected bytes.
'-f FIELD-LIST'
'--fields=FIELD-LIST'
Select for printing only the fields listed in FIELD-LIST. Fields
are separated by a TAB character by default. Also print any line
that contains no delimiter character, unless the '--only-delimited'
('-s') option is specified.
Note 'awk' supports more sophisticated field processing, and by
default will use (and discard) runs of blank characters to separate
fields, and ignore leading and trailing blanks.
awk '{print $2}' # print the second field
awk '{print $NF-1}' # print the penultimate field
awk '{print $2,$1}' # reorder the first two fields
In the unlikely event that 'awk' is unavailable, one can use the
'join' command, to process blank characters as 'awk' does above.
join -a1 -o 1.2 - /dev/null # print the second field
join -a1 -o 1.2,1.1 - /dev/null # reorder the first two fields
'-d INPUT_DELIM_BYTE'
'--delimiter=INPUT_DELIM_BYTE'
With '-f', use the first byte of INPUT_DELIM_BYTE as the input
fields separator (default is TAB).
'-n'
Do not split multi-byte characters (no-op for now).
'-s'
'--only-delimited'
For '-f', do not print lines that do not contain the field
separator character. Normally, any line without a field separator
is printed verbatim.
'--output-delimiter=OUTPUT_DELIM_STRING'
With '-f', output fields are separated by OUTPUT_DELIM_STRING. The
default with '-f' is to use the input delimiter. When using '-b'
or '-c' to select ranges of byte or character offsets (as opposed
to ranges of fields), output OUTPUT_DELIM_STRING between
non-overlapping ranges of selected bytes.
'--complement'
This option is a GNU extension. Select for printing the complement
of the bytes, characters or fields selected with the '-b', '-c' or
'-f' options. In other words, do _not_ print the bytes, characters
or fields specified via those options. This option is useful when
you have many fields and want to print all but a few of them.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'date': Print or set system date and time
Synopses:
date [OPTION]... [+FORMAT]
date [-u|--utc|--universal] [ MMDDhhmm[[CC]YY][.ss] ]
Invoking 'date' with no FORMAT argument is equivalent to invoking it
with a default format that depends on the 'LC_TIME' locale category. In
the default C locale, this format is ''+%a %b %e %H:%M:%S %Z %Y'', so
the output looks like 'Thu Mar 3 13:47:51 PST 2005'.
Normally, 'date' uses the time zone rules indicated by the 'TZ'
environment variable, or the system default rules if 'TZ' is not set.
*Note Specifying the Time Zone with 'TZ': (libc)TZ Variable.
If given an argument that starts with a '+', 'date' prints the
current date and time (or the date and time specified by the '--date'
option, see below) in the format defined by that argument, which is
similar to that of the 'strftime' function. Except for conversion
specifiers, which start with '%', characters in the format string are
printed unchanged. The conversion specifiers are described below.
An exit status of zero indicates success, and a nonzero value
indicates failure.
* Menu:
* Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
* Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
* Literal conversion specifiers:: %[%nt]
* Padding and other flags:: Pad with zeros, spaces, etc.
* Setting the time:: Changing the system clock.
* Options for date:: Instead of the current time.
* Date input formats:: Specifying date strings.
* Examples of date:: Examples.
Time conversion specifiers
--------------------------
'date' conversion specifiers related to times.
'%H'
hour ('00'...'23')
'%I'
hour ('01'...'12')
'%k'
hour, space padded (' 0'...'23'); equivalent to '%_H'. This is a GNU
extension.
'%l'
hour, space padded (' 1'...'12'); equivalent to '%_I'. This is a GNU
extension.
'%M'
minute ('00'...'59')
'%N'
nanoseconds ('000000000'...'999999999'). This is a GNU extension.
'%p'
locale's equivalent of either 'AM' or 'PM'; blank in many locales.
Noon is treated as 'PM' and midnight as 'AM'.
'%P'
like '%p', except lower case. This is a GNU extension.
'%r'
locale's 12-hour clock time (e.g., '11:11:04 PM')
'%R'
24-hour hour and minute. Same as '%H:%M'.
'%s'
seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC. Leap
seconds are not counted unless leap second support is available.
*Note %s-examples::, for examples. This is a GNU extension.
'%S'
second ('00'...'60'). This may be '60' if leap seconds are
supported.
'%T'
24-hour hour, minute, and second. Same as '%H:%M:%S'.
'%X'
locale's time representation (e.g., '23:13:48')
'%z'
RFC 2822/ISO 8601 style numeric time zone (e.g., '-0600' or
'+0530'), or nothing if no time zone is determinable. This value
reflects the numeric time zone appropriate for the current time,
using the time zone rules specified by the 'TZ' environment
variable. The time (and optionally, the time zone rules) can be
overridden by the '--date' option.
'%:z'
RFC 3339/ISO 8601 style numeric time zone with ':' (e.g., '-06:00'
or '+05:30'), or nothing if no time zone is determinable. This is
a GNU extension.
'%::z'
Numeric time zone to the nearest second with ':' (e.g., '-06:00:00'
or '+05:30:00'), or nothing if no time zone is determinable. This
is a GNU extension.
'%:::z'
Numeric time zone with ':' using the minimum necessary precision
(e.g., '-06', '+05:30', or '-04:56:02'), or nothing if no time zone
is determinable. This is a GNU extension.
'%Z'
alphabetic time zone abbreviation (e.g., 'EDT'), or nothing if no
time zone is determinable. See '%z' for how it is determined.
Date conversion specifiers
--------------------------
'date' conversion specifiers related to dates.
'%a'
locale's abbreviated weekday name (e.g., 'Sun')
'%A'
locale's full weekday name, variable length (e.g., 'Sunday')
'%b'
locale's abbreviated month name (e.g., 'Jan')
'%B'
locale's full month name, variable length (e.g., 'January')
'%c'
locale's date and time (e.g., 'Thu Mar 3 23:05:25 2005')
'%C'
century. This is like '%Y', except the last two digits are
omitted. For example, it is '20' if '%Y' is '2000', and is '-0' if
'%Y' is '-001'. It is normally at least two characters, but it may
be more.
'%d'
day of month (e.g., '01')
'%D'
date; same as '%m/%d/%y'
'%e'
day of month, space padded; same as '%_d'
'%F'
full date in ISO 8601 format; same as '%Y-%m-%d'. This is a good
choice for a date format, as it is standard and is easy to sort in
the usual case where years are in the range 0000...9999.
'%g'
year corresponding to the ISO week number, but without the century
(range '00' through '99'). This has the same format and value as
'%y', except that if the ISO week number (see '%V') belongs to the
previous or next year, that year is used instead.
'%G'
year corresponding to the ISO week number. This has the same
format and value as '%Y', except that if the ISO week number (see
'%V') belongs to the previous or next year, that year is used
instead. It is normally useful only if '%V' is also used; for
example, the format '%G-%m-%d' is probably a mistake, since it
combines the ISO week number year with the conventional month and
day.
'%h'
same as '%b'
'%j'
day of year ('001'...'366')
'%m'
month ('01'...'12')
'%u'
day of week ('1'...'7') with '1' corresponding to Monday
'%U'
week number of year, with Sunday as the first day of the week
('00'...'53'). Days in a new year preceding the first Sunday are in
week zero.
'%V'
ISO week number, that is, the week number of year, with Monday as
the first day of the week ('01'...'53'). If the week containing
January 1 has four or more days in the new year, then it is
considered week 1; otherwise, it is week 53 of the previous year,
and the next week is week 1. (See the ISO 8601 standard.)
'%w'
day of week ('0'...'6') with 0 corresponding to Sunday
'%W'
week number of year, with Monday as first day of week ('00'...'53').
Days in a new year preceding the first Monday are in week zero.
'%x'
locale's date representation (e.g., '12/31/99')
'%y'
last two digits of year ('00'...'99')
'%Y'
year. This is normally at least four characters, but it may be
more. Year '0000' precedes year '0001', and year '-001' precedes
year '0000'.
Literal conversion specifiers
-----------------------------
'date' conversion specifiers that produce literal strings.
'%%'
a literal %
'%n'
a newline
'%t'
a horizontal tab
Padding and other flags
-----------------------
Unless otherwise specified, 'date' normally pads numeric fields with
zeros, so that, for example, numeric months are always output as two
digits. Seconds since the epoch are not padded, though, since there is
no natural width for them.
As a GNU extension, 'date' recognizes any of the following optional
flags after the '%':
'-'
(hyphen) Do not pad the field; useful if the output is intended for
human consumption.
'_'
(underscore) Pad with spaces; useful if you need a fixed number of
characters in the output, but zeros are too distracting.
'0'
(zero) Pad with zeros even if the conversion specifier would
normally pad with spaces.
'^'
Use upper case characters if possible.
'#'
Use opposite case characters if possible. A field that is normally
upper case becomes lower case, and vice versa.
Here are some examples of padding:
date +%d/%m -d "Feb 1"
⇒ 01/02
date +%-d/%-m -d "Feb 1"
⇒ 1/2
date +%_d/%_m -d "Feb 1"
⇒ 1/ 2
As a GNU extension, you can specify the field width (after any flag,
if present) as a decimal number. If the natural size of the output of
the field has less than the specified number of characters, the result
is written right adjusted and padded to the given size. For example,
'%9B' prints the right adjusted month name in a field of width 9.
An optional modifier can follow the optional flag and width
specification. The modifiers are:
'E'
Use the locale's alternate representation for date and time. This
modifier applies to the '%c', '%C', '%x', '%X', '%y' and '%Y'
conversion specifiers. In a Japanese locale, for example, '%Ex'
might yield a date format based on the Japanese Emperors' reigns.
'O'
Use the locale's alternate numeric symbols for numbers. This
modifier applies only to numeric conversion specifiers.
If the format supports the modifier but no alternate representation
is available, it is ignored.
Setting the time
----------------
If given an argument that does not start with '+', 'date' sets the
system clock to the date and time specified by that argument (as
described below). You must have appropriate privileges to set the
system clock. Note for changes to persist across a reboot, the hardware
clock may need to be updated from the system clock, which might not
happen automatically on your system.
The argument must consist entirely of digits, which have the
following meaning:
'MM'
month
'DD'
day within month
'hh'
hour
'mm'
minute
'CC'
first two digits of year (optional)
'YY'
last two digits of year (optional)
'ss'
second (optional)
Note, the '--date' and '--set' options may not be used with an
argument in the above format. The '--universal' option may be used with
such an argument to indicate that the specified date and time are
relative to Coordinated Universal Time rather than to the local time
zone.
Options for 'date'
------------------
The program accepts the following options. Also see *note Common
options::.
'-d DATESTR'
'--date=DATESTR'
Display the date and time specified in DATESTR instead of the
current date and time. DATESTR can be in almost any common format.
It can contain month names, time zones, 'am' and 'pm', 'yesterday',
etc. For example, '--date="2004-02-27 14:19:13.489392193 +0530"'
specifies the instant of time that is 489,392,193 nanoseconds after
February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and
30 minutes east of UTC.
Note: input currently must be in locale independent format. E.g.,
the LC_TIME=C below is needed to print back the correct date in
many locales:
date -d "$(LC_TIME=C date)"
*Note Date input formats::.
'-f DATEFILE'
'--file=DATEFILE'
Parse each line in DATEFILE as with '-d' and display the resulting
date and time. If DATEFILE is '-', use standard input. This is
useful when you have many dates to process, because the system
overhead of starting up the 'date' executable many times can be
considerable.
'-I[TIMESPEC]'
'--iso-8601[=TIMESPEC]'
Display the date using the ISO 8601 format, '%Y-%m-%d'.
The argument TIMESPEC specifies the number of additional terms of
the time to include. It can be one of the following:
'auto'
Print just the date. This is the default if TIMESPEC is
omitted.
'hours'
Append the hour of the day to the date.
'minutes'
Append the hours and minutes.
'seconds'
Append the hours, minutes and seconds.
'ns'
Append the hours, minutes, seconds and nanoseconds.
If showing any time terms, then include the time zone using the
format '%z'.
'-r FILE'
'--reference=FILE'
Display the date and time of the last modification of FILE, instead
of the current date and time.
'-R'
'--rfc-822'
'--rfc-2822'
Display the date and time using the format '%a, %d %b %Y %H:%M:%S
%z', evaluated in the C locale so abbreviations are always in
English. For example:
Fri, 09 Sep 2005 13:51:39 -0700
This format conforms to Internet RFCs 2822
(ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt) and 822
(ftp://ftp.rfc-editor.org/in-notes/rfc822.txt), the current and
previous standards for Internet email.
'--rfc-3339=TIMESPEC'
Display the date using a format specified by Internet RFC 3339
(ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt). This is a subset
of the ISO 8601 format, except that it also permits applications to
use a space rather than a 'T' to separate dates from times. Unlike
the other standard formats, RFC 3339 format is always suitable as
input for the '--date' ('-d') and '--file' ('-f') options,
regardless of the current locale.
The argument TIMESPEC specifies how much of the time to include.
It can be one of the following:
'date'
Print just the full-date, e.g., '2005-09-14'. This is
equivalent to the format '%Y-%m-%d'.
'seconds'
Print the full-date and full-time separated by a space, e.g.,
'2005-09-14 00:56:06+05:30'. The output ends with a numeric
time-offset; here the '+05:30' means that local time is five
hours and thirty minutes east of UTC. This is equivalent to
the format '%Y-%m-%d %H:%M:%S%:z'.
'ns'
Like 'seconds', but also print nanoseconds, e.g., '2005-09-14
00:56:06.998458565+05:30'. This is equivalent to the format
'%Y-%m-%d %H:%M:%S.%N%:z'.
'-s DATESTR'
'--set=DATESTR'
Set the date and time to DATESTR. See '-d' above. See also *note
Setting the time::.
'-u'
'--utc'
'--universal'
Use Coordinated Universal Time (UTC) by operating as if the 'TZ'
environment variable were set to the string 'UTC0'. Coordinated
Universal Time is often called "Greenwich Mean Time" (GMT) for
historical reasons. Typically, systems ignore leap seconds and
thus implement an approximation to UTC rather than true UTC.
Date input formats
******************
First, a quote:
Our units of temporal measurement, from seconds on up to months,
are so complicated, asymmetrical and disjunctive so as to make
coherent mental reckoning in time all but impossible. Indeed, had
some tyrannical god contrived to enslave our minds to time, to make
it all but impossible for us to escape subjection to sodden
routines and unpleasant surprises, he could hardly have done better
than handing down our present system. It is like a set of
trapezoidal building blocks, with no vertical or horizontal
surfaces, like a language in which the simplest thought demands
ornate constructions, useless particles and lengthy
circumlocutions. Unlike the more successful patterns of language
and science, which enable us to face experience boldly or at least
level-headedly, our system of temporal calculation silently and
persistently encourages our terror of time.
... It is as though architects had to measure length in feet, width
in meters and height in ells; as though basic instruction manuals
demanded a knowledge of five different languages. It is no wonder
then that we often look into our own immediate past or future, last
Tuesday or a week from Sunday, with feelings of helpless confusion.
...
Robert Grudin, 'Time and the Art of Living'.
This section describes the textual date representations that GNU
programs accept. These are the strings you, as a user, can supply as
arguments to the various programs. The C interface (via the
'parse_datetime' function) is not described here.
* Menu:
* General date syntax:: Common rules.
* Calendar date items:: 19 Dec 1994.
* Time of day items:: 9:20pm.
* Time zone items:: EST, PDT, UTC, ...
* Combined date and time of day items:: 1972-09-24T20:02:00,000000-0500.
* Day of week items:: Monday and others.
* Relative items in date strings:: next tuesday, 2 years ago.
* Pure numbers in date strings:: 19931219, 1440.
* Seconds since the Epoch:: @1078100502.
* Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
* Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al.
General date syntax
A "date" is a string, possibly empty, containing many items separated by
whitespace. The whitespace may be omitted when no ambiguity arises.
The empty string means the beginning of today (i.e., midnight). Order
of the items is immaterial. A date string may contain many flavors of
items:
• calendar date items
• time of day items
• time zone items
• combined date and time of day items
• day of the week items
• relative items
• pure numbers.
We describe each of these item types in turn, below.
A few ordinal numbers may be written out in words in some contexts.
This is most useful for specifying day of the week items or relative
items (see below). Among the most commonly used ordinal numbers, the
word 'last' stands for -1, 'this' stands for 0, and 'first' and 'next'
both stand for 1. Because the word 'second' stands for the unit of time
there is no way to write the ordinal number 2, but for convenience
'third' stands for 3, 'fourth' for 4, 'fifth' for 5, 'sixth' for 6,
'seventh' for 7, 'eighth' for 8, 'ninth' for 9, 'tenth' for 10,
'eleventh' for 11 and 'twelfth' for 12.
When a month is written this way, it is still considered to be
written numerically, instead of being "spelled in full"; this changes
the allowed strings.
In the current implementation, only English is supported for words
and abbreviations like 'AM', 'DST', 'EST', 'first', 'January', 'Sunday',
'tomorrow', and 'year'.
The output of the 'date' command is not always acceptable as a date
string, not only because of the language problem, but also because there
is no standard meaning for time zone items like 'IST'. When using
'date' to generate a date string intended to be parsed later, specify a
date format that is independent of language and that does not use time
zone items other than 'UTC' and 'Z'. Here are some ways to do this:
$ LC_ALL=C TZ=UTC0 date
Mon Mar 1 00:21:42 UTC 2004
$ TZ=UTC0 date +'%Y-%m-%d %H:%M:%SZ'
2004-03-01 00:21:42Z
$ date --rfc-3339=ns # --rfc-3339 is a GNU extension.
2004-02-29 16:21:42.692722128-08:00
$ date --rfc-2822 # a GNU extension
Sun, 29 Feb 2004 16:21:42 -0800
$ date +'%Y-%m-%d %H:%M:%S %z' # %z is a GNU extension.
2004-02-29 16:21:42 -0800
$ date +'@%s.%N' # %s and %N are GNU extensions.
@1078100502.692722128
Alphabetic case is completely ignored in dates. Comments may be
introduced between round parentheses, as long as included parentheses
are properly nested. Hyphens not followed by a digit are currently
ignored. Leading zeros on numbers are ignored.
Invalid dates like '2005-02-29' or times like '24:00' are rejected.
In the typical case of a host that does not support leap seconds, a time
like '23:59:60' is rejected even if it corresponds to a valid leap
second.
Calendar date items
A "calendar date item" specifies a day of the year. It is specified
differently, depending on whether the month is specified numerically or
literally. All these strings specify the same calendar date:
1972-09-24 # ISO 8601.
72-9-24 # Assume 19xx for 69 through 99,
# 20xx for 00 through 68.
72-09-24 # Leading zeros are ignored.
9/24/72 # Common U.S. writing.
24 September 1972
24 Sept 72 # September has a special abbreviation.
24 Sep 72 # Three-letter abbreviations always allowed.
Sep 24, 1972
24-sep-72
24sep72
The year can also be omitted. In this case, the last specified year
is used, or the current year if none. For example:
9/24
sep 24
Here are the rules.
For numeric months, the ISO 8601 format 'YEAR-MONTH-DAY' is allowed,
where YEAR is any positive number, MONTH is a number between 01 and 12,
and DAY is a number between 01 and 31. A leading zero must be present
if a number is less than ten. If YEAR is 68 or smaller, then 2000 is
added to it; otherwise, if YEAR is less than 100, then 1900 is added to
it. The construct 'MONTH/DAY/YEAR', popular in the United States, is
accepted. Also 'MONTH/DAY', omitting the year.
Literal months may be spelled out in full: 'January', 'February',
'March', 'April', 'May', 'June', 'July', 'August', 'September',
'October', 'November' or 'December'. Literal months may be abbreviated
to their first three letters, possibly followed by an abbreviating dot.
It is also permitted to write 'Sept' instead of 'September'.
When months are written literally, the calendar date may be given as
any of the following:
DAY MONTH YEAR
DAY MONTH
MONTH DAY YEAR
DAY-MONTH-YEAR
Or, omitting the year:
MONTH DAY
Time of day items
A "time of day item" in date strings specifies the time on a given day.
Here are some examples, all of which represent the same time:
20:02:00.000000
20:02
8:02pm
20:02-0500 # In EST (U.S. Eastern Standard Time).
More generally, the time of day may be given as 'HOUR:MINUTE:SECOND',
where HOUR is a number between 0 and 23, MINUTE is a number between 0
and 59, and SECOND is a number between 0 and 59 possibly followed by '.'
or ',' and a fraction containing one or more digits. Alternatively,
':SECOND' can be omitted, in which case it is taken to be zero. On the
rare hosts that support leap seconds, SECOND may be 60.
If the time is followed by 'am' or 'pm' (or 'a.m.' or 'p.m.'), HOUR
is restricted to run from 1 to 12, and ':MINUTE' may be omitted (taken
to be zero). 'am' indicates the first half of the day, 'pm' indicates
the second half of the day. In this notation, 12 is the predecessor of
1: midnight is '12am' while noon is '12pm'. (This is the zero-oriented
interpretation of '12am' and '12pm', as opposed to the old tradition
derived from Latin which uses '12m' for noon and '12pm' for midnight.)
The time may alternatively be followed by a time zone correction,
expressed as 'SHHMM', where S is '+' or '-', HH is a number of zone
hours and MM is a number of zone minutes. The zone minutes term, MM,
may be omitted, in which case the one- or two-digit correction is
interpreted as a number of hours. You can also separate HH from MM with
a colon. When a time zone correction is given this way, it forces
interpretation of the time relative to Coordinated Universal Time (UTC),
overriding any previous specification for the time zone or the local
time zone. For example, '+0530' and '+05:30' both stand for the time
zone 5.5 hours ahead of UTC (e.g., India). This is the best way to
specify a time zone correction by fractional parts of an hour. The
maximum zone correction is 24 hours.
Either 'am'/'pm' or a time zone correction may be specified, but not
both.
Time zone items
A "time zone item" specifies an international time zone, indicated by a
small set of letters, e.g., 'UTC' or 'Z' for Coordinated Universal Time.
Any included periods are ignored. By following a non-daylight-saving
time zone by the string 'DST' in a separate word (that is, separated by
some white space), the corresponding daylight saving time zone may be
specified. Alternatively, a non-daylight-saving time zone can be
followed by a time zone correction, to add the two values. This is
normally done only for 'UTC'; for example, 'UTC+05:30' is equivalent to
'+05:30'.
Time zone items other than 'UTC' and 'Z' are obsolescent and are not
recommended, because they are ambiguous; for example, 'EST' has a
different meaning in Australia than in the United States. Instead, it's
better to use unambiguous numeric time zone corrections like '-0500', as
described in the previous section.
If neither a time zone item nor a time zone correction is supplied,
time stamps are interpreted using the rules of the default time zone
(*note Specifying time zone rules::).
Combined date and time of day items
The ISO 8601 date and time of day extended format consists of an ISO
8601 date, a 'T' character separator, and an ISO 8601 time of day. This
format is also recognized if the 'T' is replaced by a space.
In this format, the time of day should use 24-hour notation.
Fractional seconds are allowed, with either comma or period preceding
the fraction. ISO 8601 fractional minutes and hours are not supported.
Typically, hosts support nanosecond timestamp resolution; excess
precision is silently discarded.
Here are some examples:
2012-09-24T20:02:00.052-0500
2012-12-31T23:59:59,999999999+1100
1970-01-01 00:00Z
Day of week items
The explicit mention of a day of the week will forward the date (only if
necessary) to reach that day of the week in the future.
Days of the week may be spelled out in full: 'Sunday', 'Monday',
'Tuesday', 'Wednesday', 'Thursday', 'Friday' or 'Saturday'. Days may be
abbreviated to their first three letters, optionally followed by a
period. The special abbreviations 'Tues' for 'Tuesday', 'Wednes' for
'Wednesday' and 'Thur' or 'Thurs' for 'Thursday' are also allowed.
A number may precede a day of the week item to move forward
supplementary weeks. It is best used in expression like 'third monday'.
In this context, 'last DAY' or 'next DAY' is also acceptable; they move
one week before or after the day that DAY by itself would represent.
A comma following a day of the week item is ignored.
Relative items in date strings
"Relative items" adjust a date (or the current date if none) forward or
backward. The effects of relative items accumulate. Here are some
examples:
1 year
1 year ago
3 years
2 days
The unit of time displacement may be selected by the string 'year' or
'month' for moving by whole years or months. These are fuzzy units, as
years and months are not all of equal duration. More precise units are
'fortnight' which is worth 14 days, 'week' worth 7 days, 'day' worth 24
hours, 'hour' worth 60 minutes, 'minute' or 'min' worth 60 seconds, and
'second' or 'sec' worth one second. An 's' suffix on these units is
accepted and ignored.
The unit of time may be preceded by a multiplier, given as an
optionally signed number. Unsigned numbers are taken as positively
signed. No number at all implies 1 for a multiplier. Following a
relative item by the string 'ago' is equivalent to preceding the unit by
a multiplier with value -1.
The string 'tomorrow' is worth one day in the future (equivalent to
'day'), the string 'yesterday' is worth one day in the past (equivalent
to 'day ago').
The strings 'now' or 'today' are relative items corresponding to
zero-valued time displacement, these strings come from the fact a
zero-valued time displacement represents the current time when not
otherwise changed by previous items. They may be used to stress other
items, like in '12:00 today'. The string 'this' also has the meaning of
a zero-valued time displacement, but is preferred in date strings like
'this thursday'.
When a relative item causes the resulting date to cross a boundary
where the clocks were adjusted, typically for daylight saving time, the
resulting date and time are adjusted accordingly.
The fuzz in units can cause problems with relative items. For
example, '2003-07-31 -1 month' might evaluate to 2003-07-01, because
2003-06-31 is an invalid date. To determine the previous month more
reliably, you can ask for the month before the 15th of the current
month. For example:
$ date -R
Thu, 31 Jul 2003 13:02:39 -0700
$ date --date='-1 month' +'Last month was %B?'
Last month was July?
$ date --date="$(date +%Y-%m-15) -1 month" +'Last month was %B!'
Last month was June!
Also, take care when manipulating dates around clock changes such as
daylight saving leaps. In a few cases these have added or subtracted as
much as 24 hours from the clock, so it is often wise to adopt universal
time by setting the 'TZ' environment variable to 'UTC0' before embarking
on calendrical calculations.
Pure numbers in date strings
The precise interpretation of a pure decimal number depends on the
context in the date string.
If the decimal number is of the form YYYYMMDD and no other calendar
date item (*note Calendar date items::) appears before it in the date
string, then YYYY is read as the year, MM as the month number and DD as
the day of the month, for the specified calendar date.
If the decimal number is of the form HHMM and no other time of day
item appears before it in the date string, then HH is read as the hour
of the day and MM as the minute of the hour, for the specified time of
day. MM can also be omitted.
If both a calendar date and a time of day appear to the left of a
number in the date string, but no relative item, then the number
overrides the year.
Seconds since the Epoch
If you precede a number with '@', it represents an internal time stamp
as a count of seconds. The number can contain an internal decimal point
(either '.' or ','); any excess precision not supported by the internal
representation is truncated toward minus infinity. Such a number cannot
be combined with any other date item, as it specifies a complete time
stamp.
Internally, computer times are represented as a count of seconds
since an epoch—a well-defined point of time. On GNU and POSIX systems,
the epoch is 1970-01-01 00:00:00 UTC, so '@0' represents this time, '@1'
represents 1970-01-01 00:00:01 UTC, and so forth. GNU and most other
POSIX-compliant systems support such times as an extension to POSIX,
using negative counts, so that '@-1' represents 1969-12-31 23:59:59 UTC.
Traditional Unix systems count seconds with 32-bit two's-complement
integers and can represent times from 1901-12-13 20:45:52 through
2038-01-19 03:14:07 UTC. More modern systems use 64-bit counts of
seconds with nanosecond subcounts, and can represent all the times in
the known lifetime of the universe to a resolution of 1 nanosecond.
On most hosts, these counts ignore the presence of leap seconds. For
example, on most hosts '@915148799' represents 1998-12-31 23:59:59 UTC,
'@915148800' represents 1999-01-01 00:00:00 UTC, and there is no way to
represent the intervening leap second 1998-12-31 23:59:60 UTC.
Specifying time zone rules
Normally, dates are interpreted using the rules of the current time
zone, which in turn are specified by the 'TZ' environment variable, or
by a system default if 'TZ' is not set. To specify a different set of
default time zone rules that apply just to one date, start the date with
a string of the form 'TZ="RULE"'. The two quote characters ('"') must
be present in the date, and any quotes or backslashes within RULE must
be escaped by a backslash.
For example, with the GNU 'date' command you can answer the question
"What time is it in New York when a Paris clock shows 6:30am on October
31, 2004?" by using a date beginning with 'TZ="Europe/Paris"' as shown
in the following shell transcript:
$ export TZ="America/New_York"
$ date --date='TZ="Europe/Paris" 2004-10-31 06:30'
Sun Oct 31 01:30:00 EDT 2004
In this example, the '--date' operand begins with its own 'TZ'
setting, so the rest of that operand is processed according to
'Europe/Paris' rules, treating the string '2004-10-31 06:30' as if it
were in Paris. However, since the output of the 'date' command is
processed according to the overall time zone rules, it uses New York
time. (Paris was normally six hours ahead of New York in 2004, but this
example refers to a brief Halloween period when the gap was five hours.)
A 'TZ' value is a rule that typically names a location in the 'tz'
database (http://www.twinsun.com/tz/tz-link.htm). A recent catalog of
location names appears in the TWiki Date and Time Gateway
(http://twiki.org/cgi-bin/xtra/tzdate). A few non-GNU hosts require a
colon before a location name in a 'TZ' setting, e.g.,
'TZ=":America/New_York"'.
The 'tz' database includes a wide variety of locations ranging from
'Arctic/Longyearbyen' to 'Antarctica/South_Pole', but if you are at sea
and have your own private time zone, or if you are using a non-GNU host
that does not support the 'tz' database, you may need to use a POSIX
rule instead. Simple POSIX rules like 'UTC0' specify a time zone
without daylight saving time; other rules can specify simple daylight
saving regimes. *Note Specifying the Time Zone with 'TZ': (libc)TZ
Variable.
Authors of 'parse_datetime'
'parse_datetime' started life as 'getdate', as originally implemented by
Steven M. Bellovin (<smb@research.att.com>) while at the University of
North Carolina at Chapel Hill. The code was later tweaked by a couple
of people on Usenet, then completely overhauled by Rich $alz
(<rsalz@bbn.com>) and Jim Berets (<jberets@bbn.com>) in August, 1990.
Various revisions for the GNU system were made by David MacKenzie, Jim
Meyering, Paul Eggert and others, including renaming it to 'get_date' to
avoid a conflict with the alternative Posix function 'getdate', and a
later rename to 'parse_datetime'. The Posix function 'getdate' can
parse more locale-specific dates using 'strptime', but relies on an
environment variable and external file, and lacks the thread-safety of
'parse_datetime'.
This chapter was originally produced by François Pinard
(<pinard@iro.umontreal.ca>) from the 'parse_datetime.y' source code, and
then edited by K. Berry (<kb@cs.umb.edu>).
Examples of 'date'
-------------------
Here are a few examples. Also see the documentation for the '-d' option
in the previous section.
• To print the date of the day before yesterday:
date --date='2 days ago'
• To print the date of the day three months and one day hence:
date --date='3 months 1 day'
• To print the day of year of Christmas in the current year:
date --date='25 Dec' +%j
• To print the current full month name and the day of the month:
date '+%B %d'
But this may not be what you want because for the first nine days
of the month, the '%d' expands to a zero-padded two-digit field,
for example 'date -d 1may '+%B %d'' will print 'May 01'.
• To print a date without the leading zero for one-digit days of the
month, you can use the (GNU extension) '-' flag to suppress the
padding altogether:
date -d 1may '+%B %-d
• To print the current date and time in the format required by many
non-GNU versions of 'date' when setting the system clock:
date +%m%d%H%M%Y.%S
• To set the system clock forward by two minutes:
date --set='+2 minutes'
• To print the date in RFC 2822 format, use 'date --rfc-2822'. Here
is some example output:
Fri, 09 Sep 2005 13:51:39 -0700
• To convert a date string to the number of seconds since the epoch
(which is 1970-01-01 00:00:00 UTC), use the '--date' option with
the '%s' format. That can be useful in sorting and/or graphing
and/or comparing data by date. The following command outputs the
number of the seconds since the epoch for the time two minutes
after the epoch:
date --date='1970-01-01 00:02:00 +0000' +%s
120
If you do not specify time zone information in the date string,
'date' uses your computer's idea of the time zone when interpreting
the string. For example, if your computer's time zone is that of
Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
seconds) behind UTC:
# local time zone used
date --date='1970-01-01 00:02:00' +%s
18120
• If you're sorting or graphing dated data, your raw date values may
be represented as seconds since the epoch. But few people can look
at the date '946684800' and casually note "Oh, that's the first
second of the year 2000 in Greenwich, England."
date --date='2000-01-01 UTC' +%s
946684800
An alternative is to use the '--utc' ('-u') option. Then you may
omit 'UTC' from the date string. Although this produces the same
result for '%s' and many other format sequences, with a time zone
offset different from zero, it would give a different result for
zone-dependent formats like '%z'.
date -u --date=2000-01-01 +%s
946684800
To convert such an unwieldy number of seconds back to a more
readable form, use a command like this:
# local time zone used
date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
1999-12-31 19:00:00 -0500
Or if you do not mind depending on the '@' feature present since
coreutils 5.3.0, you could shorten this to:
date -d @946684800 +"%F %T %z"
1999-12-31 19:00:00 -0500
Often it is better to output UTC-relative date and time:
date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
2000-01-01 00:00:00 +0000
• Typically the seconds count omits leap seconds, but some systems
are exceptions. Because leap seconds are not predictable, the
mapping between the seconds count and a future timestamp is not
reliable on the atypical systems that include leap seconds in their
counts.
Here is how the two kinds of systems handle the leap second at
2012-06-30 23:59:60 UTC:
# Typical systems ignore leap seconds:
date --date='2012-06-30 23:59:59 +0000' +%s
1341100799
date --date='2012-06-30 23:59:60 +0000' +%s
date: invalid date '2012-06-30 23:59:60 +0000'
date --date='2012-07-01 00:00:00 +0000' +%s
1341100800
# Atypical systems count leap seconds:
date --date='2012-06-30 23:59:59 +0000' +%s
1341100823
date --date='2012-06-30 23:59:60 +0000' +%s
1341100824
date --date='2012-07-01 00:00:00 +0000' +%s
1341100825
(coreutils)
'dd': Convert and copy a file
'dd' copies a file (from standard input to standard output, by default)
with a changeable I/O block size, while optionally performing
conversions on it. Synopses:
dd [OPERAND]...
dd OPTION
The only options are '--help' and '--version'. *Note Common
options::. 'dd' accepts the following operands, whose syntax was
inspired by the DD (data definition) statement of OS/360 JCL.
'if=FILE'
Read from FILE instead of standard input.
'of=FILE'
Write to FILE instead of standard output. Unless 'conv=notrunc' is
given, 'dd' truncates FILE to zero bytes (or the size specified
with 'seek=').
'ibs=BYTES'
Set the input block size to BYTES. This makes 'dd' read BYTES per
block. The default is 512 bytes.
'obs=BYTES'
Set the output block size to BYTES. This makes 'dd' write BYTES
per block. The default is 512 bytes.
'bs=BYTES'
Set both input and output block sizes to BYTES. This makes 'dd'
read and write BYTES per block, overriding any 'ibs' and 'obs'
settings. In addition, if no data-transforming 'conv' option is
specified, input is copied to the output as soon as it's read, even
if it is smaller than the block size.
'cbs=BYTES'
Set the conversion block size to BYTES. When converting
variable-length records to fixed-length ones ('conv=block') or the
reverse ('conv=unblock'), use BYTES as the fixed record length.
'skip=N'
Skip N 'ibs'-byte blocks in the input file before copying. If
'iflag=skip_bytes' is specified, N is interpreted as a byte count
rather than a block count.
'seek=N'
Skip N 'obs'-byte blocks in the output file before copying. if
'oflag=seek_bytes' is specified, N is interpreted as a byte count
rather than a block count.
'count=N'
Copy N 'ibs'-byte blocks from the input file, instead of everything
until the end of the file. if 'iflag=count_bytes' is specified, N
is interpreted as a byte count rather than a block count. Note if
the input may return short reads as could be the case when reading
from a pipe for example, 'iflag=fullblock' will ensure that
'count=' corresponds to complete input blocks rather than the
traditional POSIX specified behavior of counting input read
operations.
'status=WHICH'
Transfer information is normally output to stderr upon receipt of
the 'INFO' signal or when 'dd' exits. Specifying WHICH will
identify which information to suppress.
'noxfer'
Do not print the transfer rate and volume statistics that
normally make up the last status line.
'none'
Do not print any informational or warning messages to stderr.
Error messages are output as normal.
'conv=CONVERSION[,CONVERSION]...'
Convert the file as specified by the CONVERSION argument(s). (No
spaces around any comma(s).)
Conversions:
'ascii'
Convert EBCDIC to ASCII, using the conversion table specified
by POSIX. This provides a 1:1 translation for all 256 bytes.
This option implies 'conv=unblock'; input is converted to
ASCII before trailing spaces are deleted.
'ebcdic'
Convert ASCII to EBCDIC. This is the inverse of the 'ascii'
conversion. This option implies 'conv=block'; trailing spaces
are added before being converted to EBCDIC.
'ibm'
This acts like 'conv=ebcdic', except it uses the alternate
conversion table specified by POSIX. This is not a 1:1
translation, but reflects common historical practice for '~',
'[', and ']'.
The 'ascii', 'ebcdic', and 'ibm' conversions are mutually
exclusive. If you use any of these options, you should also
use the 'cbs=' option.
'block'
For each line in the input, output 'cbs' bytes, replacing the
input newline with a space and padding with spaces as
necessary.
'unblock'
Remove any trailing spaces in each 'cbs'-sized input block,
and append a newline.
The 'block' and 'unblock' conversions are mutually exclusive.
'lcase'
Change uppercase letters to lowercase.
'ucase'
Change lowercase letters to uppercase.
The 'lcase' and 'ucase' conversions are mutually exclusive.
'sparse'
Try to seek rather than write NUL output blocks. On a file
system that supports sparse files, this will create sparse
output when extending the output file. Be careful when using
this option in conjunction with 'conv=notrunc' or
'oflag=append'. With 'conv=notrunc', existing data in the
output file corresponding to NUL blocks from the input, will
be untouched. With 'oflag=append' the seeks performed will be
ineffective. Similarly, when the output is a device rather
than a file, NUL input blocks are not copied, and therefore
this option is most useful with virtual or pre zeroed devices.
'swab'
Swap every pair of input bytes. GNU 'dd', unlike others,
works when an odd number of bytes are read—the last byte is
simply copied (since there is nothing to swap it with).
'sync'
Pad every input block to size of 'ibs' with trailing zero
bytes. When used with 'block' or 'unblock', pad with spaces
instead of zero bytes.
The following "conversions" are really file flags and don't affect
internal processing:
'excl'
Fail if the output file already exists; 'dd' must create the
output file itself.
'nocreat'
Do not create the output file; the output file must already
exist.
The 'excl' and 'nocreat' conversions are mutually exclusive.
'notrunc'
Do not truncate the output file.
'noerror'
Continue after read errors.
'fdatasync'
Synchronize output data just before finishing. This forces a
physical write of output data.
'fsync'
Synchronize output data and metadata just before finishing.
This forces a physical write of output data and metadata.
'iflag=FLAG[,FLAG]...'
Access the input file using the flags specified by the FLAG
argument(s). (No spaces around any comma(s).)
'oflag=FLAG[,FLAG]...'
Access the output file using the flags specified by the FLAG
argument(s). (No spaces around any comma(s).)
Here are the flags. Not every flag is supported on every operating
system.
'append'
Write in append mode, so that even if some other process is
writing to this file, every 'dd' write will append to the
current contents of the file. This flag makes sense only for
output. If you combine this flag with the 'of=FILE' operand,
you should also specify 'conv=notrunc' unless you want the
output file to be truncated before being appended to.
'cio'
Use concurrent I/O mode for data. This mode performs direct
I/O and drops the POSIX requirement to serialize all I/O to
the same file. A file cannot be opened in CIO mode and with a
standard open at the same time.
'direct'
Use direct I/O for data, avoiding the buffer cache. Note that
the kernel may impose restrictions on read or write buffer
sizes. For example, with an ext4 destination file system and
a linux-based kernel, using 'oflag=direct' will cause writes
to fail with 'EINVAL' if the output buffer size is not a
multiple of 512.
'directory'
Fail unless the file is a directory. Most operating systems
do not allow I/O to a directory, so this flag has limited
utility.
'dsync'
Use synchronized I/O for data. For the output file, this
forces a physical write of output data on each write. For the
input file, this flag can matter when reading from a remote
file that has been written to synchronously by some other
process. Metadata (e.g., last-access and last-modified time)
is not necessarily synchronized.
'sync'
Use synchronized I/O for both data and metadata.
'nocache'
Discard the data cache for a file. When count=0 all cache is
discarded, otherwise the cache is dropped for the processed
portion of the file. Also when count=0 failure to discard the
cache is diagnosed and reflected in the exit status. Here as
some usage examples:
# Advise to drop cache for whole file
dd if=ifile iflag=nocache count=0
# Ensure drop cache for the whole file
dd of=ofile oflag=nocache conv=notrunc,fdatasync count=0
# Drop cache for part of file
dd if=ifile iflag=nocache skip=10 count=10 of=/dev/null
# Stream data using just the read-ahead cache
dd if=ifile of=ofile iflag=nocache oflag=nocache
'nonblock'
Use non-blocking I/O.
'noatime'
Do not update the file's access time. Some older file systems
silently ignore this flag, so it is a good idea to test it on
your files before relying on it.
'noctty'
Do not assign the file to be a controlling terminal for 'dd'.
This has no effect when the file is not a terminal. On many
hosts (e.g., GNU/Linux hosts), this option has no effect at
all.
'nofollow'
Do not follow symbolic links.
'nolinks'
Fail if the file has multiple hard links.
'binary'
Use binary I/O. This option has an effect only on nonstandard
platforms that distinguish binary from text I/O.
'text'
Use text I/O. Like 'binary', this option has no effect on
standard platforms.
'fullblock'
Accumulate full blocks from input. The 'read' system call may
return early if a full block is not available. When that
happens, continue calling 'read' to fill the remainder of the
block. This flag can be used only with 'iflag'. This flag is
useful with pipes for example as they may return short reads.
In that case, this flag is needed to ensure that a 'count='
argument is interpreted as a block count rather than a count
of read operations.
'count_bytes'
Interpret the 'count=' operand as a byte count, rather than a
block count, which allows specifying a length that is not a
multiple of the I/O block size. This flag can be used only
with 'iflag'.
'skip_bytes'
Interpret the 'skip=' operand as a byte count, rather than a
block count, which allows specifying an offset that is not a
multiple of the I/O block size. This flag can be used only
with 'iflag'.
'seek_bytes'
Interpret the 'seek=' operand as a byte count, rather than a
block count, which allows specifying an offset that is not a
multiple of the I/O block size. This flag can be used only
with 'oflag'.
These flags are not supported on all systems, and 'dd' rejects
attempts to use them when they are not supported. When reading
from standard input or writing to standard output, the 'nofollow'
and 'noctty' flags should not be specified, and the other flags
(e.g., 'nonblock') can affect how other processes behave with the
affected file descriptors, even after 'dd' exits.
The numeric-valued strings above (N and BYTES) can be followed by a
multiplier: 'b'=512, 'c'=1, 'w'=2, 'xM'=M, or any of the standard block
size suffixes like 'k'=1024 (*note Block size::).
Any block size you specify via 'bs=', 'ibs=', 'obs=', 'cbs=' should
not be too large—values larger than a few megabytes are generally
wasteful or (as in the gigabyte..exabyte case) downright
counterproductive or error-inducing.
To process data that is at an offset or size that is not a multiple
of the I/O block size, you can use the 'skip_bytes', 'seek_bytes' and
'count_bytes' flags. Alternatively the traditional method of separate
'dd' invocations can be used. For example, the following shell commands
copy data in 512 KiB blocks between a disk and a tape, but do not save
or restore a 4 KiB label at the start of the disk:
disk=/dev/rdsk/c0t1d0s2
tape=/dev/rmt/0
# Copy all but the label from disk to tape.
(dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
# Copy from tape back to disk, but leave the disk label alone.
(dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
For failing disks, other tools come with a great variety of extra
functionality to ease the saving of as much data as possible before the
disk finally dies, e.g. GNU 'ddrescue'
(http://www.gnu.org/software/ddrescue/). However, in some cases such a
tool is not available or the administrator feels more comfortable with
the handling of 'dd'. As a simple rescue method, call 'dd' as shown in
the following example: the options 'conv=noerror,sync' are used to
continue after read errors and to pad out bad reads with NULs, while
'iflag=fullblock' caters for short reads (which traditionally never
occur on disk based devices):
# Rescue data from an (unmounted!) partition of a failing disk.
dd conv=noerror,sync iflag=fullblock </dev/sda1 > /mnt/rescue.img
Sending an 'INFO' signal to a running 'dd' process makes it print I/O
statistics to standard error and then resume copying. In the example
below, 'dd' is run in the background to copy 10 million blocks. The
'kill' command makes it output intermediate I/O statistics, and when
'dd' completes normally or is killed by the 'SIGINT' signal, it outputs
the final statistics.
$ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
$ kill -s INFO $pid; wait $pid
3385223+0 records in
3385223+0 records out
1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
10000000+0 records in
10000000+0 records out
5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
On systems lacking the 'INFO' signal 'dd' responds to the 'USR1'
signal instead, unless the 'POSIXLY_CORRECT' environment variable is
set.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(builtin command)
declare: declare [-aAfFgilnrtux] [-p] [name[=value] ...]
Set variable values and attributes.
Declare variables and give them attributes. If no NAMEs are given,
display the attributes and values of all variables.
Options:
-f restrict action or display to function names and definitions
-F restrict display to function names only (plus line number and
source file when debugging)
-g create global variables when used in a shell function; otherwise
ignored
-p display the attributes and value of each NAME
Options which set attributes:
-a to make NAMEs indexed arrays (if supported)
-A to make NAMEs associative arrays (if supported)
-i to make NAMEs have the 'integer' attribute
-l to convert NAMEs to lower case on assignment
-n make NAME a reference to the variable named by its value
-r to make NAMEs readonly
-t to make NAMEs have the 'trace' attribute
-u to convert NAMEs to upper case on assignment
-x to make NAMEs export
Using '+' instead of '-' turns off the given attribute.
Variables with the integer attribute have arithmetic evaluation (see
the 'let' command) performed when the variable is assigned a value.
When used in a function, 'declare' makes NAMEs local, as with the 'local'
command. The '-g' option suppresses this behavior.
Exit Status:
Returns success unless an invalid option is supplied or a variable
assignment error occurs.
(coreutils)
'df': Report file system disk space usage
'df' reports the amount of disk space used and available on file
systems. Synopsis:
df [OPTION]... [FILE]...
With no arguments, 'df' reports the space used and available on all
currently mounted file systems (of all types). Otherwise, 'df' reports
on the file system containing each argument FILE.
Normally the disk space is printed in units of 1024 bytes, but this
can be overridden (*note Block size::). Non-integer quantities are
rounded up to the next higher unit.
For bind mounts and without arguments, 'df' only outputs the
statistics for that device with the shortest mount point name in the
list of file systems (MTAB), i.e., it hides duplicate entries, unless
the '-a' option is specified.
With the same logic, 'df' elides a mount entry of a dummy pseudo
device if there is another mount entry of a real block device for that
mount point with the same device number, e.g. the early-boot pseudo
file system 'rootfs' is not shown per default when already the real root
device has been mounted.
If an argument FILE resolves to a special file containing a mounted
file system, 'df' shows the space available on that file system rather
than on the file system containing the device node. GNU 'df' does not
attempt to determine the disk usage on unmounted file systems, because
on most kinds of systems doing so requires extremely nonportable
intimate knowledge of file system structures.
The program accepts the following options. Also see *note Common
options::.
'-a'
'--all'
Include in the listing dummy file systems, which are omitted by
default. Such file systems are typically special-purpose
pseudo-file-systems, such as automounter entries.
'-B SIZE'
'--block-size=SIZE'
Scale sizes by SIZE before printing them (*note Block size::). For
example, '-BG' prints sizes in units of 1,073,741,824 bytes.
'--total'
Print a grand total of all arguments after all arguments have been
processed. This can be used to find out the total disk size, usage
and available space of all listed devices.
For the grand total line, 'df' prints '"total"' into the SOURCE
column, and '"-"' into the TARGET column. If there is no SOURCE
column (see '--output'), then 'df' prints '"total"' into the TARGET
column, if present.
'-h'
'--human-readable'
Append a size letter to each size, such as 'M' for mebibytes.
Powers of 1024 are used, not 1000; 'M' stands for 1,048,576 bytes.
This option is equivalent to '--block-size=human-readable'. Use
the '--si' option if you prefer powers of 1000.
'-H'
Equivalent to '--si'.
'-i'
'--inodes'
List inode usage information instead of block usage. An inode
(short for index node) contains information about a file such as
its owner, permissions, timestamps, and location on the disk.
'-k'
Print sizes in 1024-byte blocks, overriding the default block size
(*note Block size::). This option is equivalent to
'--block-size=1K'.
'-l'
'--local'
Limit the listing to local file systems. By default, remote file
systems are also listed.
'--no-sync'
Do not invoke the 'sync' system call before getting any usage data.
This may make 'df' run significantly faster on systems with many
disks, but on some systems (notably SunOS) the results may be
slightly out of date. This is the default.
'--output'
'--output[=FIELD_LIST]'
Use the output format defined by FIELD_LIST, or print all fields if
FIELD_LIST is omitted. In the latter case, the order of the
columns conforms to the order of the field descriptions below.
The use of the '--output' together with each of the options '-i',
'-P', and '-T' is mutually exclusive.
FIELD_LIST is a comma-separated list of columns to be included in
'df''s output and therefore effectively controls the order of
output columns. Each field can thus be used at the place of
choice, but yet must only be used once.
Valid field names in the FIELD_LIST are:
'source'
The source of the mount point, usually a device.
'fstype'
File system type.
'itotal'
Total number of inodes.
'iused'
Number of used inodes.
'iavail'
Number of available inodes.
'ipcent'
Percentage of IUSED divided by ITOTAL.
'size'
Total number of blocks.
'used'
Number of used blocks.
'avail'
Number of available blocks.
'pcent'
Percentage of USED divided by SIZE.
'file'
The file name if specified on the command line.
'target'
The mount point.
The fields for block and inodes statistics are affected by the
scaling options like '-h' as usual.
The definition of the FIELD_LIST can even be splitted among several
'--output' uses.
#!/bin/sh
# Print the TARGET (i.e., the mount point) along with their percentage
# statistic regarding the blocks and the inodes.
df --out=target --output=pcent,ipcent
# Print all available fields.
df --o
'-P'
'--portability'
Use the POSIX output format. This is like the default format
except for the following:
1. The information about each file system is always printed on
exactly one line; a mount device is never put on a line by
itself. This means that if the mount device name is more than
20 characters long (e.g., for some network mounts), the
columns are misaligned.
2. The labels in the header output line are changed to conform to
POSIX.
3. The default block size and output format are unaffected by the
'DF_BLOCK_SIZE', 'BLOCK_SIZE' and 'BLOCKSIZE' environment
variables. However, the default block size is still affected
by 'POSIXLY_CORRECT': it is 512 if 'POSIXLY_CORRECT' is set,
1024 otherwise. *Note Block size::.
'--si'
Append an SI-style abbreviation to each size, such as 'M' for
megabytes. Powers of 1000 are used, not 1024; 'M' stands for
1,000,000 bytes. This option is equivalent to '--block-size=si'.
Use the '-h' or '--human-readable' option if you prefer powers of
1024.
'--sync'
Invoke the 'sync' system call before getting any usage data. On
some systems (notably SunOS), doing this yields more up to date
results, but in general this option makes 'df' much slower,
especially when there are many or very busy file systems.
'-t FSTYPE'
'--type=FSTYPE'
Limit the listing to file systems of type FSTYPE. Multiple file
system types can be specified by giving multiple '-t' options. By
default, nothing is omitted.
'-T'
'--print-type'
Print each file system's type. The types printed here are the same
ones you can include or exclude with '-t' and '-x'. The particular
types printed are whatever is supported by the system. Here are
some of the common names (this list is certainly not exhaustive):
'nfs'
An NFS file system, i.e., one mounted over a network from
another machine. This is the one type name which seems to be
used uniformly by all systems.
'ext2, ext3, ext4, xfs, btrfs...'
A file system on a locally-mounted hard disk. (The system
might even support more than one type here; Linux does.)
'iso9660, cdfs'
A file system on a CD or DVD drive. HP-UX uses 'cdfs', most
other systems use 'iso9660'.
'ntfs,fat'
File systems used by MS-Windows / MS-DOS.
'-x FSTYPE'
'--exclude-type=FSTYPE'
Limit the listing to file systems not of type FSTYPE. Multiple
file system types can be eliminated by giving multiple '-x'
options. By default, no file system types are omitted.
'-v'
Ignored; for compatibility with System V versions of 'df'.
An exit status of zero indicates success, and a nonzero value
indicates failure. Failure includes the case where no output is
generated, so you can inspect the exit status of a command like 'df -t
ext3 -t reiserfs DIR' to test whether DIR is on a file system of type
'ext3' or 'reiserfs'.
Since the list of file systems (MTAB) is needed to determine the file
system type, failure includes the cases when that list cannot be read
and one or more of the options '-a', '-l', '-t' or '-x' is used together
with a file name argument.
(coreutils)
'dir': Briefly list directory contents 'dir' is equivalent to 'ls -C -b'; that is, by default files are listed in columns, sorted vertically, and special characters are represented by backslash escape sequences. *Note 'ls': ls invocation.
(coreutils)
'dircolors': Color setup for 'ls'
'dircolors' outputs a sequence of shell commands to set up the terminal
for color output from 'ls' (and 'dir', etc.). Typical usage:
eval "$(dircolors [OPTION]... [FILE])"
If FILE is specified, 'dircolors' reads it to determine which colors
to use for which file types and extensions. Otherwise, a precompiled
database is used. For details on the format of these files, run
'dircolors --print-database'.
To make 'dircolors' read a '~/.dircolors' file if it exists, you can
put the following lines in your '~/.bashrc' (or adapt them to your
favorite shell):
d=.dircolors
test -r $d && eval "$(dircolors $d)"
The output is a shell command to set the 'LS_COLORS' environment
variable. You can specify the shell syntax to use on the command line,
or 'dircolors' will guess it from the value of the 'SHELL' environment
variable.
The program accepts the following options. Also see *note Common
options::.
'-b'
'--sh'
'--bourne-shell'
Output Bourne shell commands. This is the default if the 'SHELL'
environment variable is set and does not end with 'csh' or 'tcsh'.
'-c'
'--csh'
'--c-shell'
Output C shell commands. This is the default if 'SHELL' ends with
'csh' or 'tcsh'.
'-p'
'--print-database'
Print the (compiled-in) default color configuration database. This
output is itself a valid configuration file, and is fairly
descriptive of the possibilities.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'dirname': Strip last file name component
'dirname' prints all but the final slash-delimited component of each
NAME. Slashes on either side of the final component are also removed.
If the string contains no slash, 'dirname' prints '.' (meaning the
current directory). Synopsis:
dirname [OPTION] NAME...
NAME need not be a file name, but if it is, this operation
effectively lists the directory that contains the final component,
including the case when the final component is itself a directory.
Together, 'basename' and 'dirname' are designed such that if 'ls
"$name"' succeeds, then the command sequence 'cd "$(dirname "$name")";
ls "$(basename "$name")"' will, too. This works for everything except
file names containing a trailing newline.
POSIX allows the implementation to define the results if NAME is
'//'. With GNU 'dirname', the result is '//' on platforms where // is
distinct from /, and '/' on platforms where there is no difference.
The program accepts the following option. Also see *note Common
options::.
'-z'
'--zero'
Output a zero byte (ASCII NUL) at the end of each line, rather than
a newline. This option enables other programs to parse the output
even when that output would contain data with embedded newlines.
An exit status of zero indicates success, and a nonzero value
indicates failure.
Examples:
# Output "/usr/bin".
dirname /usr/bin/sort
dirname /usr/bin//.//
# Output "dir1" followed by "dir2"
dirname dir1/str dir2/str
# Output ".".
dirname stdio.h
(builtin command)
dirs: dirs [-clpv] [+N] [-N]
Display directory stack.
Display the list of currently remembered directories. Directories
find their way onto the list with the 'pushd' command; you can get
back up through the list with the 'popd' command.
Options:
-c clear the directory stack by deleting all of the elements
-l do not print tilde-prefixed versions of directories relative
to your home directory
-p print the directory stack with one entry per line
-v print the directory stack with one entry per line prefixed
with its position in the stack
Arguments:
+N Displays the Nth entry counting from the left of the list shown by
dirs when invoked without options, starting with zero.
-N Displays the Nth entry counting from the right of the list shown by
dirs when invoked without options, starting with zero.
Exit Status:
Returns success unless an invalid option is supplied or an error occurs.
(builtin command)
disown: disown [-h] [-ar] [jobspec ...]
Remove jobs from current shell.
Removes each JOBSPEC argument from the table of active jobs. Without
any JOBSPECs, the shell uses its notion of the current job.
Options:
-a remove all jobs if JOBSPEC is not supplied
-h mark each JOBSPEC so that SIGHUP is not sent to the job if the
shell receives a SIGHUP
-r remove only running jobs
Exit Status:
Returns success unless an invalid option or JOBSPEC is given.
(coreutils)
'du': Estimate file space usage
'du' reports the amount of disk space used by the specified files and
for each subdirectory (of directory arguments). Synopsis:
du [OPTION]... [FILE]...
With no arguments, 'du' reports the disk space for the current
directory. Normally the disk space is printed in units of 1024 bytes,
but this can be overridden (*note Block size::). Non-integer quantities
are rounded up to the next higher unit.
If two or more hard links point to the same file, only one of the
hard links is counted. The FILE argument order affects which links are
counted, and changing the argument order may change the numbers that
'du' outputs.
The program accepts the following options. Also see *note Common
options::.
'-0'
'--null'
Output a zero byte (ASCII NUL) at the end of each line, rather than
a newline. This option enables other programs to parse the output
even when that output would contain data with embedded newlines.
'-a'
'--all'
Show counts for all files, not just directories.
'--apparent-size'
Print apparent sizes, rather than disk usage. The apparent size of
a file is the number of bytes reported by 'wc -c' on regular files,
or more generally, 'ls -l --block-size=1' or 'stat --format=%s'.
For example, a file containing the word 'zoo' with no newline
would, of course, have an apparent size of 3. Such a small file
may require anywhere from 0 to 16 KiB or more of disk space,
depending on the type and configuration of the file system on which
the file resides. However, a sparse file created with this
command:
dd bs=1 seek=2GiB if=/dev/null of=big
has an apparent size of 2 GiB, yet on most modern systems, it
actually uses almost no disk space.
'-B SIZE'
'--block-size=SIZE'
Scale sizes by SIZE before printing them (*note Block size::). For
example, '-BG' prints sizes in units of 1,073,741,824 bytes.
'-b'
'--bytes'
Equivalent to '--apparent-size --block-size=1'.
'-c'
'--total'
Print a grand total of all arguments after all arguments have been
processed. This can be used to find out the total disk usage of a
given set of files or directories.
'-D'
'--dereference-args'
Dereference symbolic links that are command line arguments. Does
not affect other symbolic links. This is helpful for finding out
the disk usage of directories, such as '/usr/tmp', which are often
symbolic links.
'-d DEPTH'
'--max-depth=DEPTH'
Show the total for each directory (and file if –all) that is at
most MAX_DEPTH levels down from the root of the hierarchy. The
root is at level 0, so 'du --max-depth=0' is equivalent to 'du -s'.
'--files0-from=FILE'
Disallow processing files named on the command line, and instead
process those named in file FILE; each name being terminated by a
zero byte (ASCII NUL). This is useful when the list of file names
is so long that it may exceed a command line length limitation. In
such cases, running 'du' via 'xargs' is undesirable because it
splits the list into pieces and makes 'du' print with the '--total'
('-c') option for each sublist rather than for the entire list.
One way to produce a list of ASCII NUL terminated file names is
with GNU 'find', using its '-print0' predicate. If FILE is '-'
then the ASCII NUL terminated file names are read from standard
input.
'-H'
Equivalent to '--dereference-args' ('-D').
'-h'
'--human-readable'
Append a size letter to each size, such as 'M' for mebibytes.
Powers of 1024 are used, not 1000; 'M' stands for 1,048,576 bytes.
This option is equivalent to '--block-size=human-readable'. Use
the '--si' option if you prefer powers of 1000.
'--inodes'
List inode usage information instead of block usage. This option
is useful for finding directories which contain many files, and
therefore eat up most of the inodes space of a file system (see
'df', option '--inodes'). It can well be combined with the options
'-a', '-c', '-h', '-l', '-s', '-S', '-t' and '-x'; however, passing
other options regarding the block size, for example '-b', '-m' and
'--apparent-size', is ignored.
'-k'
Print sizes in 1024-byte blocks, overriding the default block size
(*note Block size::). This option is equivalent to
'--block-size=1K'.
'-L'
'--dereference'
Dereference symbolic links (show the disk space used by the file or
directory that the link points to instead of the space used by the
link).
'-l'
'--count-links'
Count the size of all files, even if they have appeared already (as
a hard link).
'-m'
Print sizes in 1,048,576-byte blocks, overriding the default block
size (*note Block size::). This option is equivalent to
'--block-size=1M'.
'-P'
'--no-dereference'
For each symbolic links encountered by 'du', consider the disk
space used by the symbolic link.
'-S'
'--separate-dirs'
Normally, in the output of 'du' (when not using '--summarize'), the
size listed next to a directory name, D, represents the sum of
sizes of all entries beneath D as well as the size of D itself.
With '--separate-dirs', the size reported for a directory name, D,
will exclude the size of any subdirectories.
'--si'
Append an SI-style abbreviation to each size, such as 'M' for
megabytes. Powers of 1000 are used, not 1024; 'M' stands for
1,000,000 bytes. This option is equivalent to '--block-size=si'.
Use the '-h' or '--human-readable' option if you prefer powers of
1024.
'-s'
'--summarize'
Display only a total for each argument.
'-t SIZE'
'--threshold=SIZE'
Exclude entries based on a given SIZE. The SIZE refers to used
blocks in normal mode (*note Block size::), or inodes count in
conjunction with the '--inodes' option.
If SIZE is positive, then 'du' will only print entries with a size
greater than or equal to that.
If SIZE is negative, then 'du' will only print entries with a size
smaller than or equal to that.
Although GNU 'find' can be used to find files of a certain size,
'du''s '--threshold' option can be used to also filter directories
based on a given size.
Please note that the '--threshold' option can be combined with the
'--apparent-size' option, and in this case would elide entries
based on its apparent size.
Please note that the '--threshold' option can be combined with the
'--inodes' option, and in this case would elide entries based on
its inodes count.
Here's how you would use '--threshold' to find directories with a
size greater than or equal to 200 megabytes:
du --threshold=200MB
Here's how you would use '--threshold' to find directories and
files - note the '-a' - with an apparent size smaller than or equal
to 500 bytes:
du -a -t -500 --apparent-size
Here's how you would use '--threshold' to find directories on the
root file system with more than 20000 inodes used in the directory
tree below:
du --inodes -x --threshold=20000 /
'--time'
Show time of the most recent modification of any file in the
directory, or any of its subdirectories.
'--time=ctime'
'--time=status'
'--time=use'
Show the most recent status change time (the 'ctime' in the inode)
of any file in the directory, instead of the modification time.
'--time=atime'
'--time=access'
Show the most recent access time (the 'atime' in the inode) of any
file in the directory, instead of the modification time.
'--time-style=STYLE'
List timestamps in style STYLE. This option has an effect only if
the '--time' option is also specified. The STYLE should be one of
the following:
'+FORMAT'
List timestamps using FORMAT, where FORMAT is interpreted like
the format argument of 'date' (*note date invocation::). For
example, '--time-style="+%Y-%m-%d %H:%M:%S"' causes 'du' to
list timestamps like '2002-03-30 23:45:56'. As with 'date',
FORMAT's interpretation is affected by the 'LC_TIME' locale
category.
'full-iso'
List timestamps in full using ISO 8601 date, time, and time
zone format with nanosecond precision, e.g., '2002-03-30
23:45:56.477817180 -0700'. This style is equivalent to
'+%Y-%m-%d %H:%M:%S.%N %z'.
'long-iso'
List ISO 8601 date and time in minutes, e.g., '2002-03-30
23:45'. These timestamps are shorter than 'full-iso'
timestamps, and are usually good enough for everyday work.
This style is equivalent to '+%Y-%m-%d %H:%M'.
'iso'
List ISO 8601 dates for timestamps, e.g., '2002-03-30'. This
style is equivalent to '+%Y-%m-%d'.
You can specify the default value of the '--time-style' option with
the environment variable 'TIME_STYLE'; if 'TIME_STYLE' is not set
the default style is 'long-iso'. For compatibility with 'ls', if
'TIME_STYLE' begins with '+' and contains a newline, the newline
and any later characters are ignored; if 'TIME_STYLE' begins with
'posix-' the 'posix-' is ignored; and if 'TIME_STYLE' is 'locale'
it is ignored.
'-X FILE'
'--exclude-from=FILE'
Like '--exclude', except take the patterns to exclude from FILE,
one per line. If FILE is '-', take the patterns from standard
input.
'--exclude=PATTERN'
When recursing, skip subdirectories or files matching PATTERN. For
example, 'du --exclude='*.o'' excludes files whose names end in
'.o'.
'-x'
'--one-file-system'
Skip directories that are on different file systems from the one
that the argument being processed is on.
On BSD systems, 'du' reports sizes that are half the correct values
for files that are NFS-mounted from HP-UX systems. On HP-UX systems, it
reports sizes that are twice the correct values for files that are
NFS-mounted from BSD systems. This is due to a flaw in HP-UX; it also
affects the HP-UX 'du' program.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'echo': Print a line of text
'echo' writes each given STRING to standard output, with a space between
each and a newline after the last one. Synopsis:
echo [OPTION]... [STRING]...
Due to shell aliases and built-in 'echo' functions, using an
unadorned 'echo' interactively or in a script may get you different
functionality than that described here. Invoke it via 'env' (i.e., 'env
echo ...') to avoid interference from the shell.
The program accepts the following options. Also see *note Common
options::. Options must precede operands, and the normally-special
argument '--' has no special meaning and is treated like any other
STRING.
'-n'
Do not output the trailing newline.
'-e'
Enable interpretation of the following backslash-escaped characters
in each STRING:
'\a'
alert (bell)
'\b'
backspace
'\c'
produce no further output
'\e'
escape
'\f'
form feed
'\n'
newline
'\r'
carriage return
'\t'
horizontal tab
'\v'
vertical tab
'\\'
backslash
'\0NNN'
the eight-bit value that is the octal number NNN (zero to
three octal digits), if NNN is a nine-bit value, the ninth bit
is ignored
'\NNN'
the eight-bit value that is the octal number NNN (one to three
octal digits), if NNN is a nine-bit value, the ninth bit is
ignored
'\xHH'
the eight-bit value that is the hexadecimal number HH (one or
two hexadecimal digits)
'-E'
Disable interpretation of backslash escapes in each STRING. This
is the default. If '-e' and '-E' are both specified, the last one
given takes effect.
If the 'POSIXLY_CORRECT' environment variable is set, then when
'echo''s first argument is not '-n' it outputs option-like arguments
instead of treating them as options. For example, 'echo -ne hello'
outputs '-ne hello' instead of plain 'hello'.
POSIX does not require support for any options, and says that the
behavior of 'echo' is implementation-defined if any STRING contains a
backslash or if the first argument is '-n'. Portable programs can use
the 'printf' command if they need to omit trailing newlines or output
control characters or backslashes. *Note printf invocation::.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'echo': Print a line of text
'echo' writes each given STRING to standard output, with a space between
each and a newline after the last one. Synopsis:
echo [OPTION]... [STRING]...
Due to shell aliases and built-in 'echo' functions, using an
unadorned 'echo' interactively or in a script may get you different
functionality than that described here. Invoke it via 'env' (i.e., 'env
echo ...') to avoid interference from the shell.
The program accepts the following options. Also see *note Common
options::. Options must precede operands, and the normally-special
argument '--' has no special meaning and is treated like any other
STRING.
'-n'
Do not output the trailing newline.
'-e'
Enable interpretation of the following backslash-escaped characters
in each STRING:
'\a'
alert (bell)
'\b'
backspace
'\c'
produce no further output
'\e'
escape
'\f'
form feed
'\n'
newline
'\r'
carriage return
'\t'
horizontal tab
'\v'
vertical tab
'\\'
backslash
'\0NNN'
the eight-bit value that is the octal number NNN (zero to
three octal digits), if NNN is a nine-bit value, the ninth bit
is ignored
'\NNN'
the eight-bit value that is the octal number NNN (one to three
octal digits), if NNN is a nine-bit value, the ninth bit is
ignored
'\xHH'
the eight-bit value that is the hexadecimal number HH (one or
two hexadecimal digits)
'-E'
Disable interpretation of backslash escapes in each STRING. This
is the default. If '-e' and '-E' are both specified, the last one
given takes effect.
If the 'POSIXLY_CORRECT' environment variable is set, then when
'echo''s first argument is not '-n' it outputs option-like arguments
instead of treating them as options. For example, 'echo -ne hello'
outputs '-ne hello' instead of plain 'hello'.
POSIX does not require support for any options, and says that the
behavior of 'echo' is implementation-defined if any STRING contains a
backslash or if the first argument is '-n'. Portable programs can use
the 'printf' command if they need to omit trailing newlines or output
control characters or backslashes. *Note printf invocation::.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(builtin command)
enable: enable [-a] [-dnps] [-f filename] [name ...]
Enable and disable shell builtins.
Enables and disables builtin shell commands. Disabling allows you to
execute a disk command which has the same name as a shell builtin
without using a full pathname.
Options:
-a print a list of builtins showing whether or not each is enabled
-n disable each NAME or display a list of disabled builtins
-p print the list of builtins in a reusable format
-s print only the names of Posix 'special' builtins
Options controlling dynamic loading:
-f Load builtin NAME from shared object FILENAME
-d Remove a builtin loaded with -f
Without options, each NAME is enabled.
To use the 'test' found in $PATH instead of the shell builtin
version, type 'enable -n test'.
Exit Status:
Returns success unless NAME is not a shell builtin or an error occurs.
(coreutils)
'env': Run a command in a modified environment
'env' runs a command with a modified environment. Synopses:
env [OPTION]... [NAME=VALUE]... [COMMAND [ARGS]...]
env
Operands of the form 'VARIABLE=VALUE' set the environment variable
VARIABLE to value VALUE. VALUE may be empty ('VARIABLE='). Setting a
variable to an empty value is different from unsetting it. These
operands are evaluated left-to-right, so if two operands mention the
same variable the earlier is ignored.
Environment variable names can be empty, and can contain any
characters other than '=' and ASCII NUL. However, it is wise to limit
yourself to names that consist solely of underscores, digits, and ASCII
letters, and that begin with a non-digit, as applications like the shell
do not work well with other names.
The first operand that does not contain the character '=' specifies
the program to invoke; it is searched for according to the 'PATH'
environment variable. Any remaining arguments are passed as arguments
to that program. The program should not be a special built-in utility
(*note Special built-in utilities::).
Modifications to 'PATH' take effect prior to searching for COMMAND.
Use caution when reducing 'PATH'; behavior is not portable when 'PATH'
is undefined or omits key directories such as '/bin'.
In the rare case that a utility contains a '=' in the name, the only
way to disambiguate it from a variable assignment is to use an
intermediate command for COMMAND, and pass the problematic program name
via ARGS. For example, if './prog=' is an executable in the current
'PATH':
env prog= true # runs 'true', with prog= in environment
env ./prog= true # runs 'true', with ./prog= in environment
env -- prog= true # runs 'true', with prog= in environment
env sh -c '\prog= true' # runs 'prog=' with argument 'true'
env sh -c 'exec "$@"' sh prog= true # also runs 'prog='
If no command name is specified following the environment
specifications, the resulting environment is printed. This is like
specifying the 'printenv' program.
For some examples, suppose the environment passed to 'env' contains
'LOGNAME=rms', 'EDITOR=emacs', and 'PATH=.:/gnubin:/hacks':
• Output the current environment.
$ env | LC_ALL=C sort
EDITOR=emacs
LOGNAME=rms
PATH=.:/gnubin:/hacks
• Run 'foo' with a reduced environment, preserving only the original
'PATH' to avoid problems in locating 'foo'.
env - PATH="$PATH" foo
• Run 'foo' with the environment containing 'LOGNAME=rms',
'EDITOR=emacs', and 'PATH=.:/gnubin:/hacks', and guarantees that
'foo' was found in the file system rather than as a shell built-in.
env foo
• Run 'nemacs' with the environment containing 'LOGNAME=foo',
'EDITOR=emacs', 'PATH=.:/gnubin:/hacks', and 'DISPLAY=gnu:0'.
env DISPLAY=gnu:0 LOGNAME=foo nemacs
• Attempt to run the program '/energy/--' (as that is the only
possible path search result); if the command exists, the
environment will contain 'LOGNAME=rms' and 'PATH=/energy', and the
arguments will be 'e=mc2', 'bar', and 'baz'.
env -u EDITOR PATH=/energy -- e=mc2 bar baz
The program accepts the following options. Also see *note Common
options::. Options must precede operands.
'-0'
'--null'
Output a zero byte (ASCII NUL) at the end of each line, rather than
a newline. This option enables other programs to parse the output
even when that output would contain data with embedded newlines.
'-u NAME'
'--unset=NAME'
Remove variable NAME from the environment, if it was in the
environment.
'-'
'-i'
'--ignore-environment'
Start with an empty environment, ignoring the inherited
environment.
Exit status:
0 if no COMMAND is specified and the environment is output
125 if 'env' itself fails
126 if COMMAND is found but cannot be invoked
127 if COMMAND cannot be found
the exit status of COMMAND otherwise
(builtin command)
eval: eval [arg ...]
Execute arguments as a shell command.
Combine ARGs into a single string, use the result as input to the shell,
and execute the resulting commands.
Exit Status:
Returns exit status of command or success if command is null.
(builtin command)
exec: exec [-cl] [-a name] [command [arguments ...]] [redirection ...]
Replace the shell with the given command.
Execute COMMAND, replacing this shell with the specified program.
ARGUMENTS become the arguments to COMMAND. If COMMAND is not specified,
any redirections take effect in the current shell.
Options:
-a name pass NAME as the zeroth argument to COMMAND
-c execute COMMAND with an empty environment
-l place a dash in the zeroth argument to COMMAND
If the command cannot be executed, a non-interactive shell exits, unless
the shell option 'execfail' is set.
Exit Status:
Returns success unless COMMAND is not found or a redirection error occurs.
(builtin command)
exit: exit [n]
Exit the shell.
Exits the shell with a status of N. If N is omitted, the exit status
is that of the last command executed.
(coreutils)
'expand': Convert tabs to spaces
'expand' writes the contents of each given FILE, or standard input if
none are given or for a FILE of '-', to standard output, with tab
characters converted to the appropriate number of spaces. Synopsis:
expand [OPTION]... [FILE]...
By default, 'expand' converts all tabs to spaces. It preserves
backspace characters in the output; they decrement the column count for
tab calculations. The default action is equivalent to '-t 8' (set tabs
every 8 columns).
The program accepts the following options. Also see *note Common
options::.
'-t TAB1[,TAB2]...'
'--tabs=TAB1[,TAB2]...'
If only one tab stop is given, set the tabs TAB1 spaces apart
(default is 8). Otherwise, set the tabs at columns TAB1, TAB2, ...
(numbered from 0), and replace any tabs beyond the last tab stop
given with single spaces. Tab stops can be separated by blanks as
well as by commas.
For compatibility, GNU 'expand' also accepts the obsolete option
syntax, '-T1[,T2]...'. New scripts should use '-t T1[,T2]...' instead.
'-i'
'--initial'
Only convert initial tabs (those that precede all non-space or
non-tab characters) on each line to spaces.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(builtin command)
export: export [-fn] [name[=value] ...] or export -p
Set export attribute for shell variables.
Marks each NAME for automatic export to the environment of subsequently
executed commands. If VALUE is supplied, assign VALUE before exporting.
Options:
-f refer to shell functions
-n remove the export property from each NAME
-p display a list of all exported variables and functions
An argument of '--' disables further option processing.
Exit Status:
Returns success unless an invalid option is given or NAME is invalid.
(coreutils)
'expr': Evaluate expressions
'expr' evaluates an expression and writes the result on standard output.
Each token of the expression must be a separate argument.
Operands are either integers or strings. Integers consist of one or
more decimal digits, with an optional leading '-'. 'expr' converts
anything appearing in an operand position to an integer or a string
depending on the operation being applied to it.
Strings are not quoted for 'expr' itself, though you may need to
quote them to protect characters with special meaning to the shell,
e.g., spaces. However, regardless of whether it is quoted, a string
operand should not be a parenthesis or any of 'expr''s operators like
'+', so you cannot safely pass an arbitrary string '$str' to expr merely
by quoting it to the shell. One way to work around this is to use the
GNU extension '+', (e.g., '+ "$str" = foo'); a more portable way is to
use '" $str"' and to adjust the rest of the expression to take the
leading space into account (e.g., '" $str" = " foo"').
You should not pass a negative integer or a string with leading '-'
as 'expr''s first argument, as it might be misinterpreted as an option;
this can be avoided by parenthesization. Also, portable scripts should
not use a string operand that happens to take the form of an integer;
this can be worked around by inserting leading spaces as mentioned
above.
Operators may be given as infix symbols or prefix keywords.
Parentheses may be used for grouping in the usual manner. You must
quote parentheses and many operators to avoid the shell evaluating them,
however.
When built with support for the GNU MP library, 'expr' uses
arbitrary-precision arithmetic; otherwise, it uses native arithmetic
types and may fail due to arithmetic overflow.
The only options are '--help' and '--version'. *Note Common
options::. Options must precede operands.
Exit status:
0 if the expression is neither null nor 0,
1 if the expression is null or 0,
2 if the expression is invalid,
3 if an internal error occurred (e.g., arithmetic overflow).
* Menu:
* String expressions:: + : match substr index length
* Numeric expressions:: + - * / %
* Relations for expr:: | & < <= = == != >= >
* Examples of expr:: Examples.
String expressions
------------------
'expr' supports pattern matching and other string operators. These have
higher precedence than both the numeric and relational operators (in the
next sections).
'STRING : REGEX'
Perform pattern matching. The arguments are converted to strings
and the second is considered to be a (basic, a la GNU 'grep')
regular expression, with a '^' implicitly prepended. The first
argument is then matched against this regular expression.
If the match succeeds and REGEX uses '\(' and '\)', the ':'
expression returns the part of STRING that matched the
subexpression; otherwise, it returns the number of characters
matched.
If the match fails, the ':' operator returns the null string if
'\(' and '\)' are used in REGEX, otherwise 0.
Only the first '\( ... \)' pair is relevant to the return value;
additional pairs are meaningful only for grouping the regular
expression operators.
In the regular expression, '\+', '\?', and '\|' are operators which
respectively match one or more, zero or one, or separate
alternatives. SunOS and other 'expr''s treat these as regular
characters. (POSIX allows either behavior.) *Note Regular
Expression Library: (regex)Top, for details of regular expression
syntax. Some examples are in *note Examples of expr::.
'match STRING REGEX'
An alternative way to do pattern matching. This is the same as
'STRING : REGEX'.
'substr STRING POSITION LENGTH'
Returns the substring of STRING beginning at POSITION with length
at most LENGTH. If either POSITION or LENGTH is negative, zero, or
non-numeric, returns the null string.
'index STRING CHARSET'
Returns the first position in STRING where the first character in
CHARSET was found. If no character in CHARSET is found in STRING,
return 0.
'length STRING'
Returns the length of STRING.
'+ TOKEN'
Interpret TOKEN as a string, even if it is a keyword like MATCH or
an operator like '/'. This makes it possible to test 'expr length
+ "$x"' or 'expr + "$x" : '.*/\(.\)'' and have it do the right
thing even if the value of $X happens to be (for example) '/' or
'index'. This operator is a GNU extension. Portable shell scripts
should use '" $token" : ' \(.*\)'' instead of '+ "$token"'.
To make 'expr' interpret keywords as strings, you must use the
'quote' operator.
Numeric expressions
-------------------
'expr' supports the usual numeric operators, in order of increasing
precedence. These numeric operators have lower precedence than the
string operators described in the previous section, and higher
precedence than the connectives (next section).
'+ -'
Addition and subtraction. Both arguments are converted to
integers; an error occurs if this cannot be done.
'* / %'
Multiplication, division, remainder. Both arguments are converted
to integers; an error occurs if this cannot be done.
Relations for 'expr'
--------------------
'expr' supports the usual logical connectives and relations. These have
lower precedence than the string and numeric operators (previous
sections). Here is the list, lowest-precedence operator first.
'|'
Returns its first argument if that is neither null nor zero,
otherwise its second argument if it is neither null nor zero,
otherwise 0. It does not evaluate its second argument if its first
argument is neither null nor zero.
'&'
Return its first argument if neither argument is null or zero,
otherwise 0. It does not evaluate its second argument if its first
argument is null or zero.
'< <= = == != >= >'
Compare the arguments and return 1 if the relation is true, 0
otherwise. '==' is a synonym for '='. 'expr' first tries to
convert both arguments to integers and do a numeric comparison; if
either conversion fails, it does a lexicographic comparison using
the character collating sequence specified by the 'LC_COLLATE'
locale.
Examples of using 'expr'
------------------------
Here are a few examples, including quoting for shell metacharacters.
To add 1 to the shell variable 'foo', in Bourne-compatible shells:
foo=$(expr $foo + 1)
To print the non-directory part of the file name stored in '$fname',
which need not contain a '/':
expr $fname : '.*/\(.*\)' '|' $fname
An example showing that '\+' is an operator:
expr aaa : 'a\+'
⇒ 3
expr abc : 'a\(.\)c'
⇒ b
expr index abcdef cz
⇒ 3
expr index index a
error→ expr: syntax error
expr index + index a
⇒ 0
(coreutils)
'factor': Print prime factors
'factor' prints prime factors. Synopses:
factor [NUMBER]...
factor OPTION
If no NUMBER is specified on the command line, 'factor' reads numbers
from standard input, delimited by newlines, tabs, or spaces.
The 'factor' command supports only a small number of options:
'--help'
Print a short help on standard output, then exit without further
processing.
'--version'
Print the program version on standard output, then exit without
further processing.
Factoring the product of the eighth and ninth Mersenne primes takes
about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
M8=$(echo 2^31-1|bc)
M9=$(echo 2^61-1|bc)
n=$(echo "$M8 * $M9" | bc)
/usr/bin/time -f %U factor $n
4951760154835678088235319297: 2147483647 2305843009213693951
0.03
Similarly, factoring the eighth Fermat number 2^{256}+1 takes about
20 seconds on the same machine.
Factoring large numbers is, in general, hard. The Pollard Rho
algorithm used by 'factor' is particularly effective for numbers with
relatively small factors. If you wish to factor large numbers which do
not have small factors (for example, numbers which are the product of
two large primes), other methods are far better.
If 'factor' is built without using GNU MP, only single-precision
arithmetic is available, and so large numbers (typically 2^{64} and
above) will not be supported. The single-precision code uses an
algorithm which is designed for factoring smaller numbers.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'false': Do nothing, unsuccessfully 'false' does nothing except return an exit status of 1, meaning "failure". It can be used as a place holder in shell scripts where an unsuccessful command is needed. In most modern shells, 'false' is a built-in command, so when you use 'false' in a script, you're probably using the built-in command, not the one documented here. 'false' honors the '--help' and '--version' options. This version of 'false' is implemented as a C program, and is thus more secure and faster than a shell script implementation, and may safely be used as a dummy shell for the purpose of disabling accounts. Note that 'false' (unlike all other programs documented herein) exits unsuccessfully, even when invoked with '--help' or '--version'. Portable programs should not assume that the exit status of 'false' is 1, as it is greater than 1 on some non-GNU hosts.
(coreutils)
'false': Do nothing, unsuccessfully 'false' does nothing except return an exit status of 1, meaning "failure". It can be used as a place holder in shell scripts where an unsuccessful command is needed. In most modern shells, 'false' is a built-in command, so when you use 'false' in a script, you're probably using the built-in command, not the one documented here. 'false' honors the '--help' and '--version' options. This version of 'false' is implemented as a C program, and is thus more secure and faster than a shell script implementation, and may safely be used as a dummy shell for the purpose of disabling accounts. Note that 'false' (unlike all other programs documented herein) exits unsuccessfully, even when invoked with '--help' or '--version'. Portable programs should not assume that the exit status of 'false' is 1, as it is greater than 1 on some non-GNU hosts.
(builtin command)
fc: fc [-e ename] [-lnr] [first] [last] or fc -s [pat=rep] [command]
Display or execute commands from the history list.
fc is used to list or edit and re-execute commands from the history list.
FIRST and LAST can be numbers specifying the range, or FIRST can be a
string, which means the most recent command beginning with that
string.
Options:
-e ENAME select which editor to use. Default is FCEDIT, then EDITOR,
then vi
-l list lines instead of editing
-n omit line numbers when listing
-r reverse the order of the lines (newest listed first)
With the 'fc -s [pat=rep ...] [command]' format, COMMAND is
re-executed after the substitution OLD=NEW is performed.
A useful alias to use with this is r='fc -s', so that typing 'r cc'
runs the last command beginning with 'cc' and typing 'r' re-executes
the last command.
Exit Status:
Returns success or status of executed command; non-zero if an error occurs.
(builtin command)
fg: fg [job_spec]
Move job to the foreground.
Place the job identified by JOB_SPEC in the foreground, making it the
current job. If JOB_SPEC is not present, the shell's notion of the
current job is used.
Exit Status:
Status of command placed in foreground, or failure if an error occurs.
(coreutils)
'fmt': Reformat paragraph text
'fmt' fills and joins lines to produce output lines of (at most) a given
number of characters (75 by default). Synopsis:
fmt [OPTION]... [FILE]...
'fmt' reads from the specified FILE arguments (or standard input if
none are given), and writes to standard output.
By default, blank lines, spaces between words, and indentation are
preserved in the output; successive input lines with different
indentation are not joined; tabs are expanded on input and introduced on
output.
'fmt' prefers breaking lines at the end of a sentence, and tries to
avoid line breaks after the first word of a sentence or before the last
word of a sentence. A "sentence break" is defined as either the end of
a paragraph or a word ending in any of '.?!', followed by two spaces or
end of line, ignoring any intervening parentheses or quotes. Like TeX,
'fmt' reads entire "paragraphs" before choosing line breaks; the
algorithm is a variant of that given by Donald E. Knuth and Michael F.
Plass in "Breaking Paragraphs Into Lines", 'Software—Practice &
Experience' 11, 11 (November 1981), 1119–1184.
The program accepts the following options. Also see *note Common
options::.
'-c'
'--crown-margin'
"Crown margin" mode: preserve the indentation of the first two
lines within a paragraph, and align the left margin of each
subsequent line with that of the second line.
'-t'
'--tagged-paragraph'
"Tagged paragraph" mode: like crown margin mode, except that if
indentation of the first line of a paragraph is the same as the
indentation of the second, the first line is treated as a one-line
paragraph.
'-s'
'--split-only'
Split lines only. Do not join short lines to form longer ones.
This prevents sample lines of code, and other such "formatted" text
from being unduly combined.
'-u'
'--uniform-spacing'
Uniform spacing. Reduce spacing between words to one space, and
spacing between sentences to two spaces.
'-WIDTH'
'-w WIDTH'
'--width=WIDTH'
Fill output lines up to WIDTH characters (default 75 or GOAL plus
10, if GOAL is provided).
'-g GOAL'
'--goal=GOAL'
'fmt' initially tries to make lines GOAL characters wide. By
default, this is 7% shorter than WIDTH.
'-p PREFIX'
'--prefix=PREFIX'
Only lines beginning with PREFIX (possibly preceded by whitespace)
are subject to formatting. The prefix and any preceding whitespace
are stripped for the formatting and then re-attached to each
formatted output line. One use is to format certain kinds of
program comments, while leaving the code unchanged.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'fold': Wrap input lines to fit in specified width
'fold' writes each FILE ('-' means standard input), or standard input if
none are given, to standard output, breaking long lines. Synopsis:
fold [OPTION]... [FILE]...
By default, 'fold' breaks lines wider than 80 columns. The output is
split into as many lines as necessary.
'fold' counts screen columns by default; thus, a tab may count more
than one column, backspace decreases the column count, and carriage
return sets the column to zero.
The program accepts the following options. Also see *note Common
options::.
'-b'
'--bytes'
Count bytes rather than columns, so that tabs, backspaces, and
carriage returns are each counted as taking up one column, just
like other characters.
'-s'
'--spaces'
Break at word boundaries: the line is broken after the last blank
before the maximum line length. If the line contains no such
blanks, the line is broken at the maximum line length as usual.
'-w WIDTH'
'--width=WIDTH'
Use a maximum line length of WIDTH columns instead of 80.
For compatibility 'fold' supports an obsolete option syntax
'-WIDTH'. New scripts should use '-w WIDTH' instead.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(reserved word)
for: for NAME [in WORDS ... ] ; do COMMANDS; done
Execute commands for each member in a list.
The 'for' loop executes a sequence of commands for each member in a
list of items. If 'in WORDS ...;' is not present, then 'in "$@"' is
assumed. For each element in WORDS, NAME is set to that element, and
the COMMANDS are executed.
Exit Status:
Returns the status of the last command executed.
(reserved word)
function: function name { COMMANDS ; } or name () { COMMANDS ; }
Define shell function.
Create a shell function named NAME. When invoked as a simple command,
NAME runs COMMANDs in the calling shell's context. When NAME is invoked,
the arguments are passed to the function as $1...$n, and the function's
name is in $FUNCNAME.
Exit Status:
Returns success unless NAME is readonly.
(builtin command)
getopts: getopts optstring name [arg]
Parse option arguments.
Getopts is used by shell procedures to parse positional parameters
as options.
OPTSTRING contains the option letters to be recognized; if a letter
is followed by a colon, the option is expected to have an argument,
which should be separated from it by white space.
Each time it is invoked, getopts will place the next option in the
shell variable $name, initializing name if it does not exist, and
the index of the next argument to be processed into the shell
variable OPTIND. OPTIND is initialized to 1 each time the shell or
a shell script is invoked. When an option requires an argument,
getopts places that argument into the shell variable OPTARG.
getopts reports errors in one of two ways. If the first character
of OPTSTRING is a colon, getopts uses silent error reporting. In
this mode, no error messages are printed. If an invalid option is
seen, getopts places the option character found into OPTARG. If a
required argument is not found, getopts places a ':' into NAME and
sets OPTARG to the option character found. If getopts is not in
silent mode, and an invalid option is seen, getopts places '?' into
NAME and unsets OPTARG. If a required argument is not found, a '?'
is placed in NAME, OPTARG is unset, and a diagnostic message is
printed.
If the shell variable OPTERR has the value 0, getopts disables the
printing of error messages, even if the first character of
OPTSTRING is not a colon. OPTERR has the value 1 by default.
Getopts normally parses the positional parameters ($0 - $9), but if
more arguments are given, they are parsed instead.
Exit Status:
Returns success if an option is found; fails if the end of options is
encountered or an error occurs.
(coreutils)
'groups': Print group names a user is in
'groups' prints the names of the primary and any supplementary groups
for each given USERNAME, or the current process if no names are given.
If more than one name is given, the name of each user is printed before
the list of that user's groups and the user name is separated from the
group list by a colon. Synopsis:
groups [USERNAME]...
The group lists are equivalent to the output of the command 'id -Gn'.
The only options are '--help' and '--version'. *Note Common
options::.
Primary and supplementary groups for a process are normally inherited
from its parent and are usually unchanged since login. This means that
if you change the group database after logging in, 'groups' will not
reflect your changes within your existing login session. Running
'groups' with a list of users causes the user and group database to be
consulted afresh, and so will give a different result.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(builtin command)
hash: hash [-lr] [-p pathname] [-dt] [name ...]
Remember or display program locations.
Determine and remember the full pathname of each command NAME. If
no arguments are given, information about remembered commands is displayed.
Options:
-d forget the remembered location of each NAME
-l display in a format that may be reused as input
-p pathname use PATHNAME as the full pathname of NAME
-r forget all remembered locations
-t print the remembered location of each NAME, preceding
each location with the corresponding NAME if multiple
NAMEs are given
Arguments:
NAME Each NAME is searched for in $PATH and added to the list
of remembered commands.
Exit Status:
Returns success unless NAME is not found or an invalid option is given.
(coreutils)
'head': Output the first part of files
'head' prints the first part (10 lines by default) of each FILE; it
reads from standard input if no files are given or when given a FILE of
'-'. Synopsis:
head [OPTION]... [FILE]...
If more than one FILE is specified, 'head' prints a one-line header
consisting of:
==> FILE NAME <==
before the output for each FILE.
The program accepts the following options. Also see *note Common
options::.
'-c K'
'--bytes=K'
Print the first K bytes, instead of initial lines. However, if K
starts with a '-', print all but the last K bytes of each file. K
may be, or may be an integer optionally followed by, one of the
following multiplicative suffixes:
'b' => 512 ("blocks")
'KB' => 1000 (KiloBytes)
'K' => 1024 (KibiBytes)
'MB' => 1000*1000 (MegaBytes)
'M' => 1024*1024 (MebiBytes)
'GB' => 1000*1000*1000 (GigaBytes)
'G' => 1024*1024*1024 (GibiBytes)
and so on for 'T', 'P', 'E', 'Z', and 'Y'.
'-n K'
'--lines=K'
Output the first K lines. However, if K starts with a '-', print
all but the last K lines of each file. Size multiplier suffixes
are the same as with the '-c' option.
'-q'
'--quiet'
'--silent'
Never print file name headers.
'-v'
'--verbose'
Always print file name headers.
For compatibility 'head' also supports an obsolete option syntax
'-COUNTOPTIONS', which is recognized only if it is specified first.
COUNT is a decimal number optionally followed by a size letter ('b',
'k', 'm') as in '-c', or 'l' to mean count by lines, or other option
letters ('cqv'). Scripts intended for standard hosts should use '-c
COUNT' or '-n COUNT' instead. If your script must also run on hosts
that support only the obsolete syntax, it is usually simpler to avoid
'head', e.g., by using 'sed 5q' instead of 'head -5'.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(builtin command)
help: help [-dms] [pattern ...]
Display information about builtin commands.
Displays brief summaries of builtin commands. If PATTERN is
specified, gives detailed help on all commands matching PATTERN,
otherwise the list of help topics is printed.
Options:
-d output short description for each topic
-m display usage in pseudo-manpage format
-s output only a short usage synopsis for each topic matching
PATTERN
Arguments:
PATTERN Pattern specifiying a help topic
Exit Status:
Returns success unless PATTERN is not found or an invalid option is given.
(builtin command)
history: history [-c] [-d offset] [n] or history -anrw [filename] or history -ps arg [arg...]
Display or manipulate the history list.
Display the history list with line numbers, prefixing each modified
entry with a '*'. An argument of N lists only the last N entries.
Options:
-c clear the history list by deleting all of the entries
-d offset delete the history entry at offset OFFSET.
-a append history lines from this session to the history file
-n read all history lines not already read from the history file
-r read the history file and append the contents to the history
list
-w write the current history to the history file
and append them to the history list
-p perform history expansion on each ARG and display the result
without storing it in the history list
-s append the ARGs to the history list as a single entry
If FILENAME is given, it is used as the history file. Otherwise,
if $HISTFILE has a value, that is used, else ~/.bash_history.
If the $HISTTIMEFORMAT variable is set and not null, its value is used
as a format string for strftime(3) to print the time stamp associated
with each displayed history entry. No time stamps are printed otherwise.
Exit Status:
Returns success unless an invalid option is given or an error occurs.
(coreutils)
'hostid': Print numeric host identifier
'hostid' prints the numeric identifier of the current host in
hexadecimal. This command accepts no arguments. The only options are
'--help' and '--version'. *Note Common options::.
For example, here's what it prints on one system I use:
$ hostid
1bac013d
On that system, the 32-bit quantity happens to be closely related to
the system's Internet address, but that isn't always the case.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'hostname': Print or set system name
With no arguments, 'hostname' prints the name of the current host
system. With one argument, it sets the current host name to the
specified string. You must have appropriate privileges to set the host
name. Synopsis:
hostname [NAME]
The only options are '--help' and '--version'. *Note Common
options::.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'id': Print user identity
'id' prints information about the given user, or the process running it
if no user is specified. Synopsis:
id [OPTION]... [USER]
USER can be either a user ID or a name, with name look-up taking
precedence unless the ID is specified with a leading '+'. *Note
Disambiguating names and IDs::.
By default, it prints the real user ID, real group ID, effective user
ID if different from the real user ID, effective group ID if different
from the real group ID, and supplemental group IDs. In addition, if
SELinux is enabled and the 'POSIXLY_CORRECT' environment variable is not
set, then print 'context=C', where C is the security context.
Each of these numeric values is preceded by an identifying string and
followed by the corresponding user or group name in parentheses.
The options cause 'id' to print only part of the above information.
Also see *note Common options::.
'-g'
'--group'
Print only the group ID.
'-G'
'--groups'
Print only the group ID and the supplementary groups.
'-n'
'--name'
Print the user or group name instead of the ID number. Requires
'-u', '-g', or '-G'.
'-r'
'--real'
Print the real, instead of effective, user or group ID. Requires
'-u', '-g', or '-G'.
'-u'
'--user'
Print only the user ID.
'-Z'
'--context'
Print only the security context of the process, which is generally
the user's security context inherited from the parent process. If
neither SELinux or SMACK is enabled then print a warning and set
the exit status to 1.
'-z'
'--zero'
Delimit output items with NUL characters. This option is not
permitted when using the default format.
Example:
$ id -Gn --zero
users <NUL> devs <NUL>
Primary and supplementary groups for a process are normally inherited
from its parent and are usually unchanged since login. This means that
if you change the group database after logging in, 'id' will not reflect
your changes within your existing login session. Running 'id' with a
user argument causes the user and group database to be consulted afresh,
and so will give a different result.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(reserved word)
if: if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMANDS; ]... [ else COMMANDS; ] fi
Execute commands based on conditional.
The 'if COMMANDS' list is executed. If its exit status is zero, then the
'then COMMANDS' list is executed. Otherwise, each 'elif COMMANDS' list is
executed in turn, and if its exit status is zero, the corresponding
'then COMMANDS' list is executed and the if command completes. Otherwise,
the 'else COMMANDS' list is executed, if present. The exit status of the
entire construct is the exit status of the last command executed, or zero
if no condition tested true.
Exit Status:
Returns the status of the last command executed.
(coreutils)
'install': Copy files and set attributes
'install' copies files while setting their file mode bits and, if
possible, their owner and group. Synopses:
install [OPTION]... [-T] SOURCE DEST
install [OPTION]... SOURCE... DIRECTORY
install [OPTION]... -t DIRECTORY SOURCE...
install [OPTION]... -d DIRECTORY...
• If two file names are given, 'install' copies the first file to the
second.
• If the '--target-directory' ('-t') option is given, or failing that
if the last file is a directory and the '--no-target-directory'
('-T') option is not given, 'install' copies each SOURCE file to
the specified directory, using the SOURCEs' names.
• If the '--directory' ('-d') option is given, 'install' creates each
DIRECTORY and any missing parent directories. Parent directories
are created with mode 'u=rwx,go=rx' (755), regardless of the '-m'
option or the current umask. *Note Directory Setuid and Setgid::,
for how the set-user-ID and set-group-ID bits of parent directories
are inherited.
'install' is similar to 'cp', but allows you to control the
attributes of destination files. It is typically used in Makefiles to
copy programs into their destination directories. It refuses to copy
files onto themselves.
'install' never preserves extended attributes (xattr).
The program accepts the following options. Also see *note Common
options::.
'-b'
'--backup[=METHOD]'
*Note Backup options::. Make a backup of each file that would
otherwise be overwritten or removed.
'-C'
'--compare'
Compare each pair of source and destination files, and if the
destination has identical content and any specified owner, group,
permissions, and possibly SELinux context, then do not modify the
destination at all. Note this option is best used in conjunction
with '--user', '--group' and '--mode' options, lest 'install'
incorrectly determines the default attributes that installed files
would have (as it doesn't consider setgid directories and POSIX
default ACLs for example). This could result in redundant copies
or attributes that are not reset to the correct defaults.
'-c'
Ignored; for compatibility with old Unix versions of 'install'.
'-D'
Create any missing parent directories of DEST, then copy SOURCE to
DEST. Explicitly specifying the '--target-directory=DIR' will
similarly ensure the presence of that hierarchy before copying
SOURCE arguments.
'-d'
'--directory'
Create any missing parent directories, giving them the default
attributes. Then create each given directory, setting their owner,
group and mode as given on the command line or to the defaults.
'-g GROUP'
'--group=GROUP'
Set the group ownership of installed files or directories to GROUP.
The default is the process's current group. GROUP may be either a
group name or a numeric group ID.
'-m MODE'
'--mode=MODE'
Set the file mode bits for the installed file or directory to MODE,
which can be either an octal number, or a symbolic mode as in
'chmod', with 'a=' (no access allowed to anyone) as the point of
departure (*note File permissions::). The default mode is
'u=rwx,go=rx,a-s'—read, write, and execute for the owner, read and
execute for group and other, and with set-user-ID and set-group-ID
disabled. This default is not quite the same as '755', since it
disables instead of preserving set-user-ID and set-group-ID on
directories. *Note Directory Setuid and Setgid::.
'-o OWNER'
'--owner=OWNER'
If 'install' has appropriate privileges (is run as root), set the
ownership of installed files or directories to OWNER. The default
is 'root'. OWNER may be either a user name or a numeric user ID.
'--preserve-context'
Preserve the SELinux security context of files and directories.
Failure to preserve the context in all of the files or directories
will result in an exit status of 1. If SELinux is disabled then
print a warning and ignore the option.
'-p'
'--preserve-timestamps'
Set the time of last access and the time of last modification of
each installed file to match those of each corresponding original
file. When a file is installed without this option, its last
access and last modification times are both set to the time of
installation. This option is useful if you want to use the last
modification times of installed files to keep track of when they
were last built as opposed to when they were last installed.
'-s'
'--strip'
Strip the symbol tables from installed binary executables.
'--strip-program=PROGRAM'
Program used to strip binaries.
'-S SUFFIX'
'--suffix=SUFFIX'
Append SUFFIX to each backup file made with '-b'. *Note Backup
options::.
'-t DIRECTORY'
'--target-directory=DIRECTORY'
Specify the destination DIRECTORY. *Note Target directory::.
'-T'
'--no-target-directory'
Do not treat the last operand specially when it is a directory or a
symbolic link to a directory. *Note Target directory::.
'-v'
'--verbose'
Print the name of each file before copying it.
'-Z'
'--context[=CONTEXT]'
Without a specified CONTEXT, adjust the SELinux security context
according to the system default type for destination files,
similarly to the 'restorecon' command. The long form of this
option with a specific context specified, will set the context for
newly created files only. With a specified context, if both
SELinux and SMACK are disabled, a warning is issued. This option
is mutually exclusive with the '--preserve-context' option.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(builtin command)
jobs: jobs [-lnprs] [jobspec ...] or jobs -x command [args]
Display status of jobs.
Lists the active jobs. JOBSPEC restricts output to that job.
Without options, the status of all active jobs is displayed.
Options:
-l lists process IDs in addition to the normal information
-n lists only processes that have changed status since the last
notification
-p lists process IDs only
-r restrict output to running jobs
-s restrict output to stopped jobs
If -x is supplied, COMMAND is run after all job specifications that
appear in ARGS have been replaced with the process ID of that job's
process group leader.
Exit Status:
Returns success unless an invalid option is given or an error occurs.
If -x is used, returns the exit status of COMMAND.
(coreutils)
'join': Join lines on a common field
'join' writes to standard output a line for each pair of input lines
that have identical join fields. Synopsis:
join [OPTION]... FILE1 FILE2
Either FILE1 or FILE2 (but not both) can be '-', meaning standard
input. FILE1 and FILE2 should be sorted on the join fields.
Normally, the sort order is that of the collating sequence specified
by the 'LC_COLLATE' locale. Unless the '-t' option is given, the sort
comparison ignores blanks at the start of the join field, as in 'sort
-b'. If the '--ignore-case' option is given, the sort comparison
ignores the case of characters in the join field, as in 'sort -f'.
The 'sort' and 'join' commands should use consistent locales and
options if the output of 'sort' is fed to 'join'. You can use a command
like 'sort -k 1b,1' to sort a file on its default join field, but if you
select a non-default locale, join field, separator, or comparison
options, then you should do so consistently between 'join' and 'sort'.
If 'join -t ''' is specified then the whole line is considered which
matches the default operation of sort.
If the input has no unpairable lines, a GNU extension is available;
the sort order can be any order that considers two fields to be equal if
and only if the sort comparison described above considers them to be
equal. For example:
$ cat file1
a a1
c c1
b b1
$ cat file2
a a2
c c2
b b2
$ join file1 file2
a a1 a2
c c1 c2
b b1 b2
If the '--check-order' option is given, unsorted inputs will cause a
fatal error message. If the option '--nocheck-order' is given, unsorted
inputs will never cause an error message. If neither of these options
is given, wrongly sorted inputs are diagnosed only if an input file is
found to contain unpairable lines, and when both input files are non
empty. If an input file is diagnosed as being unsorted, the 'join'
command will exit with a nonzero status (and the output should not be
used).
Forcing 'join' to process wrongly sorted input files containing
unpairable lines by specifying '--nocheck-order' is not guaranteed to
produce any particular output. The output will probably not correspond
with whatever you hoped it would be.
The defaults are:
• the join field is the first field in each line;
• fields in the input are separated by one or more blanks, with
leading blanks on the line ignored;
• fields in the output are separated by a space;
• each output line consists of the join field, the remaining fields
from FILE1, then the remaining fields from FILE2.
The program accepts the following options. Also see *note Common
options::.
'-a FILE-NUMBER'
Print a line for each unpairable line in file FILE-NUMBER (either
'1' or '2'), in addition to the normal output.
'--check-order'
Fail with an error message if either input file is wrongly ordered.
'--nocheck-order'
Do not check that both input files are in sorted order. This is
the default.
'-e STRING'
Replace those output fields that are missing in the input with
STRING. I.e., missing fields specified with the '-12jo' options.
'--header'
Treat the first line of each input file as a header line. The
header lines will be joined and printed as the first output line.
If '-o' is used to specify output format, the header line will be
printed according to the specified format. The header lines will
not be checked for ordering even if '--check-order' is specified.
Also if the header lines from each file do not match, the heading
fields from the first file will be used.
'-i'
'--ignore-case'
Ignore differences in case when comparing keys. With this option,
the lines of the input files must be ordered in the same way. Use
'sort -f' to produce this ordering.
'-1 FIELD'
Join on field FIELD (a positive integer) of file 1.
'-2 FIELD'
Join on field FIELD (a positive integer) of file 2.
'-j FIELD'
Equivalent to '-1 FIELD -2 FIELD'.
'-o FIELD-LIST'
'-o auto'
If the keyword 'auto' is specified, infer the output format from
the first line in each file. This is the same as the default
output format but also ensures the same number of fields are output
for each line. Missing fields are replaced with the '-e' option
and extra fields are discarded.
Otherwise, construct each output line according to the format in
FIELD-LIST. Each element in FIELD-LIST is either the single
character '0' or has the form M.N where the file number, M, is '1'
or '2' and N is a positive field number.
A field specification of '0' denotes the join field. In most
cases, the functionality of the '0' field spec may be reproduced
using the explicit M.N that corresponds to the join field.
However, when printing unpairable lines (using either of the '-a'
or '-v' options), there is no way to specify the join field using
M.N in FIELD-LIST if there are unpairable lines in both files. To
give 'join' that functionality, POSIX invented the '0' field
specification notation.
The elements in FIELD-LIST are separated by commas or blanks.
Blank separators typically need to be quoted for the shell. For
example, the commands 'join -o 1.2,2.2' and 'join -o '1.2 2.2'' are
equivalent.
All output lines—including those printed because of any -a or -v
option—are subject to the specified FIELD-LIST.
'-t CHAR'
Use character CHAR as the input and output field separator. Treat
as significant each occurrence of CHAR in the input file. Use
'sort -t CHAR', without the '-b' option of 'sort', to produce this
ordering. If 'join -t ''' is specified, the whole line is
considered, matching the default operation of sort. If '-t '\0''
is specified then the ASCII NUL character is used to delimit the
fields.
'-v FILE-NUMBER'
Print a line for each unpairable line in file FILE-NUMBER (either
'1' or '2'), instead of the normal output.
'-z'
'--zero-terminated'
Delimit items with a zero byte rather than a newline (ASCII LF).
I.e., treat input as items separated by ASCII NUL and terminate
output items with ASCII NUL. This option can be useful in
conjunction with 'perl -0' or 'find -print0' and 'xargs -0' which
do the same in order to reliably handle arbitrary file names (even
those containing blanks or other special characters).
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'kill': Send a signal to processes
The 'kill' command sends a signal to processes, causing them to
terminate or otherwise act upon receiving the signal in some way.
Alternatively, it lists information about signals. Synopses:
kill [-s SIGNAL | --signal SIGNAL | -SIGNAL] PID...
kill [-l | --list | -t | --table] [SIGNAL]...
Due to shell aliases and built-in 'kill' functions, using an
unadorned 'kill' interactively or in a script may get you different
functionality than that described here. Invoke it via 'env' (i.e., 'env
kill ...') to avoid interference from the shell.
The first form of the 'kill' command sends a signal to all PID
arguments. The default signal to send if none is specified is 'TERM'.
The special signal number '0' does not denote a valid signal, but can be
used to test whether the PID arguments specify processes to which a
signal could be sent.
If PID is positive, the signal is sent to the process with the
process ID PID. If PID is zero, the signal is sent to all processes in
the process group of the current process. If PID is −1, the signal is
sent to all processes for which the user has permission to send a
signal. If PID is less than −1, the signal is sent to all processes in
the process group that equals the absolute value of PID.
If PID is not positive, a system-dependent set of system processes is
excluded from the list of processes to which the signal is sent.
If a negative PID argument is desired as the first one, it should be
preceded by '--'. However, as a common extension to POSIX, '--' is not
required with 'kill -SIGNAL -PID'. The following commands are
equivalent:
kill -15 -1
kill -TERM -1
kill -s TERM -- -1
kill -- -1
The first form of the 'kill' command succeeds if every PID argument
specifies at least one process that the signal was sent to.
The second form of the 'kill' command lists signal information.
Either the '-l' or '--list' option, or the '-t' or '--table' option must
be specified. Without any SIGNAL argument, all supported signals are
listed. The output of '-l' or '--list' is a list of the signal names,
one per line; if SIGNAL is already a name, the signal number is printed
instead. The output of '-t' or '--table' is a table of signal numbers,
names, and descriptions. This form of the 'kill' command succeeds if
all SIGNAL arguments are valid and if there is no output error.
The 'kill' command also supports the '--help' and '--version'
options. *Note Common options::.
A SIGNAL may be a signal name like 'HUP', or a signal number like
'1', or an exit status of a process terminated by the signal. A signal
name can be given in canonical form or prefixed by 'SIG'. The case of
the letters is ignored, except for the '-SIGNAL' option which must use
upper case to avoid ambiguity with lower case option letters. *Note
Signal specifications::, for a list of supported signal names and
numbers.
(coreutils)
'kill': Send a signal to processes
The 'kill' command sends a signal to processes, causing them to
terminate or otherwise act upon receiving the signal in some way.
Alternatively, it lists information about signals. Synopses:
kill [-s SIGNAL | --signal SIGNAL | -SIGNAL] PID...
kill [-l | --list | -t | --table] [SIGNAL]...
Due to shell aliases and built-in 'kill' functions, using an
unadorned 'kill' interactively or in a script may get you different
functionality than that described here. Invoke it via 'env' (i.e., 'env
kill ...') to avoid interference from the shell.
The first form of the 'kill' command sends a signal to all PID
arguments. The default signal to send if none is specified is 'TERM'.
The special signal number '0' does not denote a valid signal, but can be
used to test whether the PID arguments specify processes to which a
signal could be sent.
If PID is positive, the signal is sent to the process with the
process ID PID. If PID is zero, the signal is sent to all processes in
the process group of the current process. If PID is −1, the signal is
sent to all processes for which the user has permission to send a
signal. If PID is less than −1, the signal is sent to all processes in
the process group that equals the absolute value of PID.
If PID is not positive, a system-dependent set of system processes is
excluded from the list of processes to which the signal is sent.
If a negative PID argument is desired as the first one, it should be
preceded by '--'. However, as a common extension to POSIX, '--' is not
required with 'kill -SIGNAL -PID'. The following commands are
equivalent:
kill -15 -1
kill -TERM -1
kill -s TERM -- -1
kill -- -1
The first form of the 'kill' command succeeds if every PID argument
specifies at least one process that the signal was sent to.
The second form of the 'kill' command lists signal information.
Either the '-l' or '--list' option, or the '-t' or '--table' option must
be specified. Without any SIGNAL argument, all supported signals are
listed. The output of '-l' or '--list' is a list of the signal names,
one per line; if SIGNAL is already a name, the signal number is printed
instead. The output of '-t' or '--table' is a table of signal numbers,
names, and descriptions. This form of the 'kill' command succeeds if
all SIGNAL arguments are valid and if there is no output error.
The 'kill' command also supports the '--help' and '--version'
options. *Note Common options::.
A SIGNAL may be a signal name like 'HUP', or a signal number like
'1', or an exit status of a process terminated by the signal. A signal
name can be given in canonical form or prefixed by 'SIG'. The case of
the letters is ignored, except for the '-SIGNAL' option which must use
upper case to avoid ambiguity with lower case option letters. *Note
Signal specifications::, for a list of supported signal names and
numbers.
(builtin command)
let: let arg [arg ...]
Evaluate arithmetic expressions.
Evaluate each ARG as an arithmetic expression. Evaluation is done in
fixed-width integers with no check for overflow, though division by 0
is trapped and flagged as an error. The following list of operators is
grouped into levels of equal-precedence operators. The levels are listed
in order of decreasing precedence.
id++, id-- variable post-increment, post-decrement
++id, --id variable pre-increment, pre-decrement
-, + unary minus, plus
!, ~ logical and bitwise negation
** exponentiation
*, /, % multiplication, division, remainder
+, - addition, subtraction
<<, >> left and right bitwise shifts
<=, >=, <, > comparison
==, != equality, inequality
& bitwise AND
^ bitwise XOR
| bitwise OR
&& logical AND
|| logical OR
expr ? expr : expr
conditional operator
=, *=, /=, %=,
+=, -=, <<=, >>=,
&=, ^=, |= assignment
Shell variables are allowed as operands. The name of the variable
is replaced by its value (coerced to a fixed-width integer) within
an expression. The variable need not have its integer attribute
turned on to be used in an expression.
Operators are evaluated in order of precedence. Sub-expressions in
parentheses are evaluated first and may override the precedence
rules above.
Exit Status:
If the last ARG evaluates to 0, let returns 1; let returns 0 otherwise.
(coreutils)
'link': Make a hard link via the link syscall
'link' creates a single hard link at a time. It is a minimalist
interface to the system-provided 'link' function. *Note (libc)Hard
Links::. It avoids the bells and whistles of the more commonly-used
'ln' command (*note ln invocation::). Synopsis:
link FILENAME LINKNAME
FILENAME must specify an existing file, and LINKNAME must specify a
nonexistent entry in an existing directory. 'link' simply calls 'link
(FILENAME, LINKNAME)' to create the link.
On a GNU system, this command acts like 'ln --directory
--no-target-directory FILENAME LINKNAME'. However, the '--directory'
and '--no-target-directory' options are not specified by POSIX, and the
'link' command is more portable in practice.
If FILENAME is a symbolic link, it is unspecified whether LINKNAME
will be a hard link to the symbolic link or to the target of the
symbolic link. Use 'ln -P' or 'ln -L' to specify which behavior is
desired.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'ln': Make links between files
'ln' makes links between files. By default, it makes hard links; with
the '-s' option, it makes symbolic (or "soft") links. Synopses:
ln [OPTION]... [-T] TARGET LINKNAME
ln [OPTION]... TARGET
ln [OPTION]... TARGET... DIRECTORY
ln [OPTION]... -t DIRECTORY TARGET...
• If two file names are given, 'ln' creates a link to the first file
from the second.
• If one TARGET is given, 'ln' creates a link to that file in the
current directory.
• If the '--target-directory' ('-t') option is given, or failing that
if the last file is a directory and the '--no-target-directory'
('-T') option is not given, 'ln' creates a link to each TARGET file
in the specified directory, using the TARGETs' names.
Normally 'ln' does not remove existing files. Use the '--force'
('-f') option to remove them unconditionally, the '--interactive' ('-i')
option to remove them conditionally, and the '--backup' ('-b') option to
rename them.
A "hard link" is another name for an existing file; the link and the
original are indistinguishable. Technically speaking, they share the
same inode, and the inode contains all the information about a
file—indeed, it is not incorrect to say that the inode _is_ the file.
Most systems prohibit making a hard link to a directory; on those where
it is allowed, only the super-user can do so (and with caution, since
creating a cycle will cause problems to many other utilities). Hard
links cannot cross file system boundaries. (These restrictions are not
mandated by POSIX, however.)
"Symbolic links" ("symlinks" for short), on the other hand, are a
special file type (which not all kernels support: System V release 3
(and older) systems lack symlinks) in which the link file actually
refers to a different file, by name. When most operations (opening,
reading, writing, and so on) are passed the symbolic link file, the
kernel automatically "dereferences" the link and operates on the target
of the link. But some operations (e.g., removing) work on the link file
itself, rather than on its target. The owner and group of a symlink are
not significant to file access performed through the link, but do have
implications on deleting a symbolic link from a directory with the
restricted deletion bit set. On the GNU system, the mode of a symlink
has no significance and cannot be changed, but on some BSD systems, the
mode can be changed and will affect whether the symlink will be
traversed in file name resolution. *Note (libc)Symbolic Links::.
Symbolic links can contain arbitrary strings; a "dangling symlink"
occurs when the string in the symlink does not resolve to a file. There
are no restrictions against creating dangling symbolic links. There are
trade-offs to using absolute or relative symlinks. An absolute symlink
always points to the same file, even if the directory containing the
link is moved. However, if the symlink is visible from more than one
machine (such as on a networked file system), the file pointed to might
not always be the same. A relative symbolic link is resolved in
relation to the directory that contains the link, and is often useful in
referring to files on the same device without regards to what name that
device is mounted on when accessed via networked machines.
When creating a relative symlink in a different location than the
current directory, the resolution of the symlink will be different than
the resolution of the same string from the current directory.
Therefore, many users prefer to first change directories to the location
where the relative symlink will be created, so that tab-completion or
other file resolution will find the same target as what will be placed
in the symlink.
The program accepts the following options. Also see *note Common
options::.
'-b'
'--backup[=METHOD]'
*Note Backup options::. Make a backup of each file that would
otherwise be overwritten or removed.
'-d'
'-F'
'--directory'
Allow users with appropriate privileges to attempt to make hard
links to directories. However, note that this will probably fail
due to system restrictions, even for the super-user.
'-f'
'--force'
Remove existing destination files.
'-i'
'--interactive'
Prompt whether to remove existing destination files.
'-L'
'--logical'
If '-s' is not in effect, and the source file is a symbolic link,
create the hard link to the file referred to by the symbolic link,
rather than the symbolic link itself.
'-n'
'--no-dereference'
Do not treat the last operand specially when it is a symbolic link
to a directory. Instead, treat it as if it were a normal file.
When the destination is an actual directory (not a symlink to one),
there is no ambiguity. The link is created in that directory. But
when the specified destination is a symlink to a directory, there
are two ways to treat the user's request. 'ln' can treat the
destination just as it would a normal directory and create the link
in it. On the other hand, the destination can be viewed as a
non-directory—as the symlink itself. In that case, 'ln' must
delete or backup that symlink before creating the new link. The
default is to treat a destination that is a symlink to a directory
just like a directory.
This option is weaker than the '--no-target-directory' ('-T')
option, so it has no effect if both options are given.
'-P'
'--physical'
If '-s' is not in effect, and the source file is a symbolic link,
create the hard link to the symbolic link itself. On platforms
where this is not supported by the kernel, this option creates a
symbolic link with identical contents; since symbolic link contents
cannot be edited, any file name resolution performed through either
link will be the same as if a hard link had been created.
'-r'
'--relative'
Make symbolic links relative to the link location.
Example:
ln -srv /a/file /tmp
'/tmp/file' -> '../a/file'
Relative symbolic links are generated based on their canonicalized
containing directory, and canonicalized targets. I.E. all symbolic
links in these file names will be resolved. *Note realpath
invocation::, which gives greater control over relative file name
generation, as demonstrated in the following example:
ln--relative() {
test "$1" = --no-symlinks && { nosym=$1; shift; }
target="$1";
test -d "$2" && link="$2/." || link="$2"
rtarget="$(realpath $nosym -m "$target" \
--relative-to "$(dirname "$link")")"
ln -s -v "$rtarget" "$link"
}
'-s'
'--symbolic'
Make symbolic links instead of hard links. This option merely
produces an error message on systems that do not support symbolic
links.
'-S SUFFIX'
'--suffix=SUFFIX'
Append SUFFIX to each backup file made with '-b'. *Note Backup
options::.
'-t DIRECTORY'
'--target-directory=DIRECTORY'
Specify the destination DIRECTORY. *Note Target directory::.
'-T'
'--no-target-directory'
Do not treat the last operand specially when it is a directory or a
symbolic link to a directory. *Note Target directory::.
'-v'
'--verbose'
Print the name of each file after linking it successfully.
If '-L' and '-P' are both given, the last one takes precedence. If
'-s' is also given, '-L' and '-P' are silently ignored. If neither
option is given, then this implementation defaults to '-P' if the system
'link' supports hard links to symbolic links (such as the GNU system),
and '-L' if 'link' follows symbolic links (such as on BSD).
An exit status of zero indicates success, and a nonzero value
indicates failure.
Examples:
Bad Example:
# Create link ../a pointing to a in that directory.
# Not really useful because it points to itself.
ln -s a ..
Better Example:
# Change to the target before creating symlinks to avoid being confused.
cd ..
ln -s adir/a .
Bad Example:
# Hard coded file names don't move well.
ln -s $(pwd)/a /some/dir/
Better Example:
# Relative file names survive directory moves and also
# work across networked file systems.
ln -s afile anotherfile
ln -s ../adir/afile yetanotherfile
(builtin command)
local: local [option] name[=value] ...
Define local variables.
Create a local variable called NAME, and give it VALUE. OPTION can
be any option accepted by 'declare'.
Local variables can only be used within a function; they are visible
only to the function where they are defined and its children.
Exit Status:
Returns success unless an invalid option is supplied, a variable
assignment error occurs, or the shell is not executing a function.
(coreutils)
'logname': Print current login name 'logname' prints the calling user's name, as found in a system-maintained file (often '/var/run/utmp' or '/etc/utmp'), and exits with a status of 0. If there is no entry for the calling process, 'logname' prints an error message and exits with a status of 1. The only options are '--help' and '--version'. *Note Common options::. An exit status of zero indicates success, and a nonzero value indicates failure.
(builtin command)
logout: logout [n]
Exit a login shell.
Exits a login shell with exit status N. Returns an error if not executed
in a login shell.
(coreutils)
'ls': List directory contents
The 'ls' program lists information about files (of any type, including
directories). Options and file arguments can be intermixed arbitrarily,
as usual.
For non-option command-line arguments that are directories, by
default 'ls' lists the contents of directories, not recursively, and
omitting files with names beginning with '.'. For other non-option
arguments, by default 'ls' lists just the file name. If no non-option
argument is specified, 'ls' operates on the current directory, acting as
if it had been invoked with a single argument of '.'.
By default, the output is sorted alphabetically, according to the
locale settings in effect.(1) If standard output is a terminal, the
output is in columns (sorted vertically) and control characters are
output as question marks; otherwise, the output is listed one per line
and control characters are output as-is.
Because 'ls' is such a fundamental program, it has accumulated many
options over the years. They are described in the subsections below;
within each section, options are listed alphabetically (ignoring case).
The division of options into the subsections is not absolute, since some
options affect more than one aspect of 'ls''s operation.
Exit status:
0 success
1 minor problems (e.g., failure to access a file or directory not
specified as a command line argument. This happens when listing a
directory in which entries are actively being removed or renamed.)
2 serious trouble (e.g., memory exhausted, invalid option, failure
to access a file or directory specified as a command line argument
or a directory loop)
Also see *note Common options::.
* Menu:
* Which files are listed::
* What information is listed::
* Sorting the output::
* Details about version sort::
* General output formatting::
* Formatting file timestamps::
* Formatting the file names::
---------- Footnotes ----------
(1) If you use a non-POSIX locale (e.g., by setting 'LC_ALL' to
'en_US'), then 'ls' may produce output that is sorted differently than
you're accustomed to. In that case, set the 'LC_ALL' environment
variable to 'C'.
Which files are listed
----------------------
These options determine which files 'ls' lists information for. By
default, 'ls' lists files and the contents of any directories on the
command line, except that in directories it ignores files whose names
start with '.'.
'-a'
'--all'
In directories, do not ignore file names that start with '.'.
'-A'
'--almost-all'
In directories, do not ignore all file names that start with '.';
ignore only '.' and '..'. The '--all' ('-a') option overrides this
option.
'-B'
'--ignore-backups'
In directories, ignore files that end with '~'. This option is
equivalent to '--ignore='*~' --ignore='.*~''.
'-d'
'--directory'
List just the names of directories, as with other types of files,
rather than listing their contents. Do not follow symbolic links
listed on the command line unless the '--dereference-command-line'
('-H'), '--dereference' ('-L'), or
'--dereference-command-line-symlink-to-dir' options are specified.
'-H'
'--dereference-command-line'
If a command line argument specifies a symbolic link, show
information for the file the link references rather than for the
link itself.
'--dereference-command-line-symlink-to-dir'
Do not dereference symbolic links, with one exception: if a command
line argument specifies a symbolic link that refers to a directory,
show information for that directory rather than for the link
itself. This is the default behavior when no other
dereferencing-related option has been specified ('--classify'
('-F'), '--directory' ('-d'), ('-l'), '--dereference' ('-L'), or
'--dereference-command-line' ('-H')).
'--group-directories-first'
Group all the directories before the files and then sort the
directories and the files separately using the selected sort key
(see –sort option). That is, this option specifies a primary sort
key, and the –sort option specifies a secondary key. However, any
use of '--sort=none' ('-U') disables this option altogether.
'--hide=PATTERN'
In directories, ignore files whose names match the shell pattern
PATTERN, unless the '--all' ('-a') or '--almost-all' ('-A') is also
given. This option acts like '--ignore=PATTERN' except that it has
no effect if '--all' ('-a') or '--almost-all' ('-A') is also given.
This option can be useful in shell aliases. For example, if 'lx'
is an alias for 'ls --hide='*~'' and 'ly' is an alias for 'ls
--ignore='*~'', then the command 'lx -A' lists the file 'README~'
even though 'ly -A' would not.
'-I PATTERN'
'--ignore=PATTERN'
In directories, ignore files whose names match the shell pattern
(not regular expression) PATTERN. As in the shell, an initial '.'
in a file name does not match a wildcard at the start of PATTERN.
Sometimes it is useful to give this option several times. For
example,
$ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
The first option ignores names of length 3 or more that start with
'.', the second ignores all two-character names that start with '.'
except '..', and the third ignores names that start with '#'.
'-L'
'--dereference'
When showing file information for a symbolic link, show information
for the file the link references rather than the link itself.
However, even with this option, 'ls' still prints the name of the
link itself, not the name of the file that the link points to.
'-R'
'--recursive'
List the contents of all directories recursively.
What information is listed
--------------------------
These options affect the information that 'ls' displays. By default,
only file names are shown.
'--author'
List each file's author when producing long format directory
listings. In GNU/Hurd, file authors can differ from their owners,
but in other operating systems the two are the same.
'-D'
'--dired'
With the long listing ('-l') format, print an additional line after
the main output:
//DIRED// BEG1 END1 BEG2 END2 ...
The BEGN and ENDN are unsigned integers that record the byte
position of the beginning and end of each file name in the output.
This makes it easy for Emacs to find the names, even when they
contain unusual characters such as space or newline, without fancy
searching.
If directories are being listed recursively ('-R'), output a
similar line with offsets for each subdirectory name:
//SUBDIRED// BEG1 END1 ...
Finally, output a line of the form:
//DIRED-OPTIONS// --quoting-style=WORD
where WORD is the quoting style (*note Formatting the file
names::).
Here is an actual example:
$ mkdir -p a/sub/deeper a/sub2
$ touch a/f1 a/f2
$ touch a/sub/deeper/file
$ ls -gloRF --dired a
a:
total 8
-rw-r--r-- 1 0 Jun 10 12:27 f1
-rw-r--r-- 1 0 Jun 10 12:27 f2
drwxr-xr-x 3 4096 Jun 10 12:27 sub/
drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
a/sub:
total 4
drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
a/sub/deeper:
total 0
-rw-r--r-- 1 0 Jun 10 12:27 file
a/sub2:
total 0
//DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
//SUBDIRED// 2 3 167 172 228 240 290 296
//DIRED-OPTIONS// --quoting-style=literal
Note that the pairs of offsets on the '//DIRED//' line above
delimit these names: 'f1', 'f2', 'sub', 'sub2', 'deeper', 'file'.
The offsets on the '//SUBDIRED//' line delimit the following
directory names: 'a', 'a/sub', 'a/sub/deeper', 'a/sub2'.
Here is an example of how to extract the fifth entry name,
'deeper', corresponding to the pair of offsets, 222 and 228:
$ ls -gloRF --dired a > out
$ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
deeper
Note that although the listing above includes a trailing slash for
the 'deeper' entry, the offsets select the name without the
trailing slash. However, if you invoke 'ls' with '--dired' along
with an option like '--escape' (aka '-b') and operate on a file
whose name contains special characters, notice that the backslash
_is_ included:
$ touch 'a b'
$ ls -blog --dired 'a b'
-rw-r--r-- 1 0 Jun 10 12:28 a\ b
//DIRED// 30 34
//DIRED-OPTIONS// --quoting-style=escape
If you use a quoting style that adds quote marks (e.g.,
'--quoting-style=c'), then the offsets include the quote marks. So
beware that the user may select the quoting style via the
environment variable 'QUOTING_STYLE'. Hence, applications using
'--dired' should either specify an explicit
'--quoting-style=literal' option (aka '-N' or '--literal') on the
command line, or else be prepared to parse the escaped names.
'--full-time'
Produce long format directory listings, and list times in full. It
is equivalent to using '--format=long' with '--time-style=full-iso'
(*note Formatting file timestamps::).
'-g'
Produce long format directory listings, but don't display owner
information.
'-G'
'--no-group'
Inhibit display of group information in a long format directory
listing. (This is the default in some non-GNU versions of 'ls', so
we provide this option for compatibility.)
'-h'
'--human-readable'
Append a size letter to each size, such as 'M' for mebibytes.
Powers of 1024 are used, not 1000; 'M' stands for 1,048,576 bytes.
This option is equivalent to '--block-size=human-readable'. Use
the '--si' option if you prefer powers of 1000.
'-i'
'--inode'
Print the inode number (also called the file serial number and
index number) of each file to the left of the file name. (This
number uniquely identifies each file within a particular file
system.)
'-l'
'--format=long'
'--format=verbose'
In addition to the name of each file, print the file type, file
mode bits, number of hard links, owner name, group name, size, and
timestamp (*note Formatting file timestamps::), normally the
modification time. Print question marks for information that
cannot be determined.
Normally the size is printed as a byte count without punctuation,
but this can be overridden (*note Block size::). For example, '-h'
prints an abbreviated, human-readable count, and
'--block-size="'1"' prints a byte count with the thousands
separator of the current locale.
For each directory that is listed, preface the files with a line
'total BLOCKS', where BLOCKS is the total disk allocation for all
files in that directory. The block size currently defaults to 1024
bytes, but this can be overridden (*note Block size::). The BLOCKS
computed counts each hard link separately; this is arguably a
deficiency.
The file type is one of the following characters:
'-'
regular file
'b'
block special file
'c'
character special file
'C'
high performance ("contiguous data") file
'd'
directory
'D'
door (Solaris 2.5 and up)
'l'
symbolic link
'M'
off-line ("migrated") file (Cray DMF)
'n'
network special file (HP-UX)
'p'
FIFO (named pipe)
'P'
port (Solaris 10 and up)
's'
socket
'?'
some other file type
The file mode bits listed are similar to symbolic mode
specifications (*note Symbolic Modes::). But 'ls' combines
multiple bits into the third character of each set of permissions
as follows:
's'
If the set-user-ID or set-group-ID bit and the corresponding
executable bit are both set.
'S'
If the set-user-ID or set-group-ID bit is set but the
corresponding executable bit is not set.
't'
If the restricted deletion flag or sticky bit, and the
other-executable bit, are both set. The restricted deletion
flag is another name for the sticky bit. *Note Mode
Structure::.
'T'
If the restricted deletion flag or sticky bit is set but the
other-executable bit is not set.
'x'
If the executable bit is set and none of the above apply.
'-'
Otherwise.
Following the file mode bits is a single character that specifies
whether an alternate access method such as an access control list
applies to the file. When the character following the file mode
bits is a space, there is no alternate access method. When it is a
printing character, then there is such a method.
GNU 'ls' uses a '.' character to indicate a file with a security
context, but no other alternate access method.
A file with any other combination of alternate access methods is
marked with a '+' character.
'-n'
'--numeric-uid-gid'
Produce long format directory listings, but display numeric user
and group IDs instead of the owner and group names.
'-o'
Produce long format directory listings, but don't display group
information. It is equivalent to using '--format=long' with
'--no-group' .
'-s'
'--size'
Print the disk allocation of each file to the left of the file
name. This is the amount of disk space used by the file, which is
usually a bit more than the file's size, but it can be less if the
file has holes.
Normally the disk allocation is printed in units of 1024 bytes, but
this can be overridden (*note Block size::).
For files that are NFS-mounted from an HP-UX system to a BSD
system, this option reports sizes that are half the correct values.
On HP-UX systems, it reports sizes that are twice the correct
values for files that are NFS-mounted from BSD systems. This is
due to a flaw in HP-UX; it also affects the HP-UX 'ls' program.
'--si'
Append an SI-style abbreviation to each size, such as 'M' for
megabytes. Powers of 1000 are used, not 1024; 'M' stands for
1,000,000 bytes. This option is equivalent to '--block-size=si'.
Use the '-h' or '--human-readable' option if you prefer powers of
1024.
'-Z'
'--context'
Display the SELinux security context or '?' if none is found. When
used with the '-l' option, print the security context to the left
of the size column.
Sorting the output
------------------
These options change the order in which 'ls' sorts the information it
outputs. By default, sorting is done by character code (e.g., ASCII
order).
'-c'
'--time=ctime'
'--time=status'
If the long listing format (e.g., '-l', '-o') is being used, print
the status change time (the 'ctime' in the inode) instead of the
modification time. When explicitly sorting by time ('--sort=time'
or '-t') or when not using a long listing format, sort according to
the status change time.
'-f'
Primarily, like '-U'—do not sort; list the files in whatever order
they are stored in the directory. But also enable '-a' (list all
files) and disable '-l', '--color', and '-s' (if they were
specified before the '-f').
'-r'
'--reverse'
Reverse whatever the sorting method is—e.g., list files in reverse
alphabetical order, youngest first, smallest first, or whatever.
'-S'
'--sort=size'
Sort by file size, largest first.
'-t'
'--sort=time'
Sort by modification time (the 'mtime' in the inode), newest first.
'-u'
'--time=atime'
'--time=access'
'--time=use'
If the long listing format (e.g., '--format=long') is being used,
print the last access time (the 'atime' in the inode). When
explicitly sorting by time ('--sort=time' or '-t') or when not
using a long listing format, sort according to the access time.
'-U'
'--sort=none'
Do not sort; list the files in whatever order they are stored in
the directory. (Do not do any of the other unrelated things that
'-f' does.) This is especially useful when listing very large
directories, since not doing any sorting can be noticeably faster.
'-v'
'--sort=version'
Sort by version name and number, lowest first. It behaves like a
default sort, except that each sequence of decimal digits is
treated numerically as an index/version number. (*Note Details
about version sort::.)
'-X'
'--sort=extension'
Sort directory contents alphabetically by file extension
(characters after the last '.'); files with no extension are sorted
first.
Details about version sort
--------------------------
Version sorting handles the fact that file names frequently include
indices or version numbers. Standard sorting usually does not produce
the order that one expects because comparisons are made on a
character-by-character basis. Version sorting is especially useful when
browsing directories that contain many files with indices/version
numbers in their names:
$ ls -1 $ ls -1v
abc.zml-1.gz abc.zml-1.gz
abc.zml-12.gz abc.zml-2.gz
abc.zml-2.gz abc.zml-12.gz
Version-sorted strings are compared such that if VER1 and VER2 are
version numbers and PREFIX and SUFFIX (SUFFIX matching the regular
expression '(\.[A-Za-z~][A-Za-z0-9~]*)*') are strings then VER1 < VER2
implies that the name composed of "PREFIX VER1 SUFFIX" sorts before
"PREFIX VER2 SUFFIX".
Note also that leading zeros of numeric parts are ignored:
$ ls -1 $ ls -1v
abc-1.007.tgz abc-1.01a.tgz
abc-1.012b.tgz abc-1.007.tgz
abc-1.01a.tgz abc-1.012b.tgz
This functionality is implemented using gnulib's 'filevercmp'
function, which has some caveats worth noting.
• 'LC_COLLATE' is ignored, which means 'ls -v' and 'sort -V' will
sort non-numeric prefixes as if the 'LC_COLLATE' locale category
was set to 'C'.
• Some suffixes will not be matched by the regular expression
mentioned above. Consequently these examples may not sort as you
expect:
abc-1.2.3.4.7z
abc-1.2.3.7z
abc-1.2.3.4.x86_64.rpm
abc-1.2.3.x86_64.rpm
General output formatting
-------------------------
These options affect the appearance of the overall output.
'-1'
'--format=single-column'
List one file per line. This is the default for 'ls' when standard
output is not a terminal.
'-C'
'--format=vertical'
List files in columns, sorted vertically. This is the default for
'ls' if standard output is a terminal. It is always the default
for the 'dir' program. GNU 'ls' uses variable width columns to
display as many files as possible in the fewest lines.
'--color [=WHEN]'
Specify whether to use color for distinguishing file types. WHEN
may be omitted, or one of:
• none - Do not use color at all. This is the default.
• auto - Only use color if standard output is a terminal.
• always - Always use color.
Specifying '--color' and no WHEN is equivalent to '--color=always'.
Piping a colorized listing through a pager like 'more' or 'less'
usually produces unreadable results. However, using 'more -f' does
seem to work.
Note that using the '--color' option may incur a noticeable
performance penalty when run in a directory with very many entries,
because the default settings require that 'ls' 'stat' every single
file it lists. However, if you would like most of the file-type
coloring but can live without the other coloring options (e.g.,
executable, orphan, sticky, other-writable, capability), use
'dircolors' to set the 'LS_COLORS' environment variable like this,
eval $(dircolors -p | perl -pe \
's/^((CAP|S[ET]|O[TR]|M|E)\w+).*/$1 00/' | dircolors -)
and on a 'dirent.d_type'-capable file system, 'ls' will perform
only one 'stat' call per command line argument.
'-F'
'--classify'
'--indicator-style=classify'
Append a character to each file name indicating the file type.
Also, for regular files that are executable, append '*'. The file
type indicators are '/' for directories, '@' for symbolic links,
'|' for FIFOs, '=' for sockets, '>' for doors, and nothing for
regular files. Do not follow symbolic links listed on the command
line unless the '--dereference-command-line' ('-H'),
'--dereference' ('-L'), or
'--dereference-command-line-symlink-to-dir' options are specified.
'--file-type'
'--indicator-style=file-type'
Append a character to each file name indicating the file type.
This is like '-F', except that executables are not marked.
'--indicator-style=WORD'
Append a character indicator with style WORD to entry names, as
follows:
'none'
Do not append any character indicator; this is the default.
'slash'
Append '/' for directories. This is the same as the '-p'
option.
'file-type'
Append '/' for directories, '@' for symbolic links, '|' for
FIFOs, '=' for sockets, and nothing for regular files. This
is the same as the '--file-type' option.
'classify'
Append '*' for executable regular files, otherwise behave as
for 'file-type'. This is the same as the '-F' or '--classify'
option.
'-k'
'--kibibytes'
Set the default block size to its normal value of 1024 bytes,
overriding any contrary specification in environment variables
(*note Block size::). This option is in turn overridden by the
'--block-size', '-h' or '--human-readable', and '--si' options.
The '-k' or '--kibibytes' option affects the per-directory block
count written by the '-l' and similar options, and the size written
by the '-s' or '--size' option. It does not affect the file size
written by '-l'.
'-m'
'--format=commas'
List files horizontally, with as many as will fit on each line,
separated by ', ' (a comma and a space).
'-p'
'--indicator-style=slash'
Append a '/' to directory names.
'-x'
'--format=across'
'--format=horizontal'
List the files in columns, sorted horizontally.
'-T COLS'
'--tabsize=COLS'
Assume that each tab stop is COLS columns wide. The default is 8.
'ls' uses tabs where possible in the output, for efficiency. If
COLS is zero, do not use tabs at all.
Some terminal emulators might not properly align columns to the
right of a TAB following a non-ASCII byte. You can avoid that
issue by using the '-T0' option or put 'TABSIZE=0' in your
environment, to tell 'ls' to align using spaces, not tabs.
'-w'
'--width=COLS'
Assume the screen is COLS columns wide. The default is taken from
the terminal settings if possible; otherwise the environment
variable 'COLUMNS' is used if it is set; otherwise the default is
80.
Formatting file timestamps
--------------------------
By default, file timestamps are listed in abbreviated form, using a date
like 'Mar 30 2002' for non-recent timestamps, and a date-without-year
and time like 'Mar 30 23:45' for recent timestamps. This format can
change depending on the current locale as detailed below.
A timestamp is considered to be "recent" if it is less than six
months old, and is not dated in the future. If a timestamp dated today
is not listed in recent form, the timestamp is in the future, which
means you probably have clock skew problems which may break programs
like 'make' that rely on file timestamps.
Time stamps are listed according to the time zone rules specified by
the 'TZ' environment variable, or by the system default rules if 'TZ' is
not set. *Note Specifying the Time Zone with 'TZ': (libc)TZ Variable.
The following option changes how file timestamps are printed.
'--time-style=STYLE'
List timestamps in style STYLE. The STYLE should be one of the
following:
'+FORMAT'
List timestamps using FORMAT, where FORMAT is interpreted like
the format argument of 'date' (*note date invocation::). For
example, '--time-style="+%Y-%m-%d %H:%M:%S"' causes 'ls' to
list timestamps like '2002-03-30 23:45:56'. As with 'date',
FORMAT's interpretation is affected by the 'LC_TIME' locale
category.
If FORMAT contains two format strings separated by a newline,
the former is used for non-recent files and the latter for
recent files; if you want output columns to line up, you may
need to insert spaces in one of the two formats.
'full-iso'
List timestamps in full using ISO 8601 date, time, and time
zone format with nanosecond precision, e.g., '2002-03-30
23:45:56.477817180 -0700'. This style is equivalent to
'+%Y-%m-%d %H:%M:%S.%N %z'.
This is useful because the time output includes all the
information that is available from the operating system. For
example, this can help explain 'make''s behavior, since GNU
'make' uses the full timestamp to determine whether a file is
out of date.
'long-iso'
List ISO 8601 date and time in minutes, e.g., '2002-03-30
23:45'. These timestamps are shorter than 'full-iso'
timestamps, and are usually good enough for everyday work.
This style is equivalent to '+%Y-%m-%d %H:%M'.
'iso'
List ISO 8601 dates for non-recent timestamps (e.g.,
'2002-03-30 '), and ISO 8601 month, day, hour, and minute for
recent timestamps (e.g., '03-30 23:45'). These timestamps are
uglier than 'long-iso' timestamps, but they carry nearly the
same information in a smaller space and their brevity helps
'ls' output fit within traditional 80-column output lines.
The following two 'ls' invocations are equivalent:
newline='
'
ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
ls -l --time-style="iso"
'locale'
List timestamps in a locale-dependent form. For example, a
Finnish locale might list non-recent timestamps like 'maalis
30 2002' and recent timestamps like 'maalis 30 23:45'.
Locale-dependent timestamps typically consume more space than
'iso' timestamps and are harder for programs to parse because
locale conventions vary so widely, but they are easier for
many people to read.
The 'LC_TIME' locale category specifies the timestamp format.
The default POSIX locale uses timestamps like 'Mar 30 2002'
and 'Mar 30 23:45'; in this locale, the following two 'ls'
invocations are equivalent:
newline='
'
ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
ls -l --time-style="locale"
Other locales behave differently. For example, in a German
locale, '--time-style="locale"' might be equivalent to
'--time-style="+%e. %b %Y $newline%e. %b %H:%M"' and might
generate timestamps like '30. Mär 2002 ' and '30. Mär 23:45'.
'posix-STYLE'
List POSIX-locale timestamps if the 'LC_TIME' locale category
is POSIX, STYLE timestamps otherwise. For example, the
'posix-long-iso' style lists timestamps like 'Mar 30 2002'
and 'Mar 30 23:45' when in the POSIX locale, and like
'2002-03-30 23:45' otherwise.
You can specify the default value of the '--time-style' option with
the environment variable 'TIME_STYLE'; if 'TIME_STYLE' is not set the
default style is 'locale'. GNU Emacs 21.3 and later use the '--dired'
option and therefore can parse any date format, but if you are using
Emacs 21.1 or 21.2 and specify a non-POSIX locale you may need to set
'TIME_STYLE="posix-long-iso"'.
To avoid certain denial-of-service attacks, timestamps that would be
longer than 1000 bytes may be treated as errors.
Formatting the file names
-------------------------
These options change how file names themselves are printed.
'-b'
'--escape'
'--quoting-style=escape'
Quote nongraphic characters in file names using alphabetic and
octal backslash sequences like those used in C.
'-N'
'--literal'
'--quoting-style=literal'
Do not quote file names. However, with 'ls' nongraphic characters
are still printed as question marks if the output is a terminal and
you do not specify the '--show-control-chars' option.
'-q'
'--hide-control-chars'
Print question marks instead of nongraphic characters in file
names. This is the default if the output is a terminal and the
program is 'ls'.
'-Q'
'--quote-name'
'--quoting-style=c'
Enclose file names in double quotes and quote nongraphic characters
as in C.
'--quoting-style=WORD'
Use style WORD to quote file names and other strings that may
contain arbitrary characters. The WORD should be one of the
following:
'literal'
Output strings as-is; this is the same as the '-N' or
'--literal' option.
'shell'
Quote strings for the shell if they contain shell
metacharacters or would cause ambiguous output. The quoting
is suitable for POSIX-compatible shells like 'bash', but it
does not always work for incompatible shells like 'csh'.
'shell-always'
Quote strings for the shell, even if they would normally not
require quoting.
'c'
Quote strings as for C character string literals, including
the surrounding double-quote characters; this is the same as
the '-Q' or '--quote-name' option.
'escape'
Quote strings as for C character string literals, except omit
the surrounding double-quote characters; this is the same as
the '-b' or '--escape' option.
'clocale'
Quote strings as for C character string literals, except use
surrounding quotation marks appropriate for the locale.
'locale'
Quote strings as for C character string literals, except use
surrounding quotation marks appropriate for the locale, and
quote 'like this' instead of "like this" in the default C
locale. This looks nicer on many displays.
You can specify the default value of the '--quoting-style' option
with the environment variable 'QUOTING_STYLE'. If that environment
variable is not set, the default value is 'literal', but this
default may change to 'shell' in a future version of this package.
'--show-control-chars'
Print nongraphic characters as-is in file names. This is the
default unless the output is a terminal and the program is 'ls'.
(builtin command)
mapfile: mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
Read lines from the standard input into an indexed array variable.
Read lines from the standard input into the indexed array variable ARRAY, or
from file descriptor FD if the -u option is supplied. The variable MAPFILE
is the default ARRAY.
Options:
-n count Copy at most COUNT lines. If COUNT is 0, all lines are copied.
-O origin Begin assigning to ARRAY at index ORIGIN. The default index is 0.
-s count Discard the first COUNT lines read.
-t Remove a trailing newline from each line read.
-u fd Read lines from file descriptor FD instead of the standard input.
-C callback Evaluate CALLBACK each time QUANTUM lines are read.
-c quantum Specify the number of lines read between each call to CALLBACK.
Arguments:
ARRAY Array variable name to use for file data.
If -C is supplied without -c, the default quantum is 5000. When
CALLBACK is evaluated, it is supplied the index of the next array
element to be assigned and the line to be assigned to that element
as additional arguments.
If not supplied with an explicit origin, mapfile will clear ARRAY before
assigning to it.
Exit Status:
Returns success unless an invalid option is given or ARRAY is readonly or
not an indexed array.
(coreutils)
'md5sum': Print or check MD5 digests
'md5sum' computes a 128-bit checksum (or "fingerprint" or
"message-digest") for each specified FILE.
Note: The MD5 digest is more reliable than a simple CRC (provided by
the 'cksum' command) for detecting accidental file corruption, as the
chances of accidentally having two files with identical MD5 are
vanishingly small. However, it should not be considered secure against
malicious tampering: although finding a file with a given MD5
fingerprint is considered infeasible at the moment, it is known how to
modify certain files, including digital certificates, so that they
appear valid when signed with an MD5 digest. For more secure hashes,
consider using SHA-2. *Note sha2 utilities::.
If a FILE is specified as '-' or if no files are given 'md5sum'
computes the checksum for the standard input. 'md5sum' can also
determine whether a file and checksum are consistent. Synopsis:
md5sum [OPTION]... [FILE]...
For each FILE, 'md5sum' outputs the MD5 checksum, a flag indicating
binary or text input mode, and the file name. If FILE contains a
backslash or newline, the line is started with a backslash, and each
problematic character in the file name is escaped with a backslash,
making the output unambiguous even in the presence of arbitrary file
names. If FILE is omitted or specified as '-', standard input is read.
The program accepts the following options. Also see *note Common
options::.
'-b'
'--binary'
Treat each input file as binary, by reading it in binary mode and
outputting a '*' flag. This is the inverse of '--text'. On
systems like GNU that do not distinguish between binary and text
files, this option merely flags each input mode as binary: the MD5
checksum is unaffected. This option is the default on systems like
MS-DOS that distinguish between binary and text files, except for
reading standard input when standard input is a terminal.
'-c'
'--check'
Read file names and checksum information (not data) from each FILE
(or from stdin if no FILE was specified) and report whether the
checksums match the contents of the named files. The input to this
mode of 'md5sum' is usually the output of a prior,
checksum-generating run of 'md5sum'. Each valid line of input
consists of an MD5 checksum, a binary/text flag, and then a file
name. Binary mode is indicated with '*', text with ' ' (space).
For each such line, 'md5sum' reads the named file and computes its
MD5 checksum. Then, if the computed message digest does not match
the one on the line with the file name, the file is noted as having
failed the test. Otherwise, the file passes the test. By default,
for each valid line, one line is written to standard output
indicating whether the named file passed the test. After all
checks have been performed, if there were any failures, a warning
is issued to standard error. Use the '--status' option to inhibit
that output. If any listed file cannot be opened or read, if any
valid line has an MD5 checksum inconsistent with the associated
file, or if no valid line is found, 'md5sum' exits with nonzero
status. Otherwise, it exits successfully.
'--quiet'
This option is useful only when verifying checksums. When
verifying checksums, don't generate an 'OK' message per
successfully checked file. Files that fail the verification are
reported in the default one-line-per-file format. If there is any
checksum mismatch, print a warning summarizing the failures to
standard error.
'--status'
This option is useful only when verifying checksums. When
verifying checksums, don't generate the default one-line-per-file
diagnostic and don't output the warning summarizing any failures.
Failures to open or read a file still evoke individual diagnostics
to standard error. If all listed files are readable and are
consistent with the associated MD5 checksums, exit successfully.
Otherwise exit with a status code indicating there was a failure.
'--tag'
Output BSD style checksums, which indicate the checksum algorithm
used. As a GNU extension, file names with problematic characters
are escaped as described above, with the same escaping indicator of
'\' at the start of the line, being used. The '--tag' option
implies binary mode, and is disallowed with '--text' mode as
supporting that would unnecessarily complicate the output format,
while providing little benefit.
'-t'
'--text'
Treat each input file as text, by reading it in text mode and
outputting a ' ' flag. This is the inverse of '--binary'. This
option is the default on systems like GNU that do not distinguish
between binary and text files. On other systems, it is the default
for reading standard input when standard input is a terminal. This
mode is never defaulted to if '--tag' is used.
'-w'
'--warn'
When verifying checksums, warn about improperly formatted MD5
checksum lines. This option is useful only if all but a few lines
in the checked input are valid.
'--strict'
When verifying checksums, if one or more input line is invalid,
exit nonzero after all warnings have been issued.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'mkdir': Make directories
'mkdir' creates directories with the specified names. Synopsis:
mkdir [OPTION]... NAME...
'mkdir' creates each directory NAME in the order given. It reports
an error if NAME already exists, unless the '-p' option is given and
NAME is a directory.
The program accepts the following options. Also see *note Common
options::.
'-m MODE'
'--mode=MODE'
Set the file permission bits of created directories to MODE, which
uses the same syntax as in 'chmod' and uses 'a=rwx' (read, write
and execute allowed for everyone) for the point of the departure.
*Note File permissions::.
Normally the directory has the desired file mode bits at the moment
it is created. As a GNU extension, MODE may also mention special
mode bits, but in this case there may be a temporary window during
which the directory exists but its special mode bits are incorrect.
*Note Directory Setuid and Setgid::, for how the set-user-ID and
set-group-ID bits of directories are inherited unless overridden in
this way.
'-p'
'--parents'
Make any missing parent directories for each argument, setting
their file permission bits to the umask modified by 'u+wx'. Ignore
existing parent directories, and do not change their file
permission bits.
To set the file permission bits of any newly-created parent
directories to a value that includes 'u+wx', you can set the umask
before invoking 'mkdir'. For example, if the shell command '(umask
u=rwx,go=rx; mkdir -p P/Q)' creates the parent 'P' it sets the
parent's permission bits to 'u=rwx,go=rx'. To set a parent's
special mode bits as well, you can invoke 'chmod' after 'mkdir'.
*Note Directory Setuid and Setgid::, for how the set-user-ID and
set-group-ID bits of newly-created parent directories are
inherited.
'-v'
'--verbose'
Print a message for each created directory. This is most useful
with '--parents'.
'-Z'
'--context[=CONTEXT]'
Without a specified CONTEXT, adjust the SELinux security context
according to the system default type for destination files,
similarly to the 'restorecon' command. The long form of this
option with a specific context specified, will set the context for
newly created files only. With a specified context, if both
SELinux and SMACK are disabled, a warning is issued.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'mkfifo': Make FIFOs (named pipes)
'mkfifo' creates FIFOs (also called "named pipes") with the specified
names. Synopsis:
mkfifo [OPTION] NAME...
A "FIFO" is a special file type that permits independent processes to
communicate. One process opens the FIFO file for writing, and another
for reading, after which data can flow as with the usual anonymous pipe
in shells or elsewhere.
The program accepts the following option. Also see *note Common
options::.
'-m MODE'
'--mode=MODE'
Set the mode of created FIFOs to MODE, which is symbolic as in
'chmod' and uses 'a=rw' (read and write allowed for everyone) for
the point of departure. MODE should specify only file permission
bits. *Note File permissions::.
'-Z'
'--context[=CONTEXT]'
Without a specified CONTEXT, adjust the SELinux security context
according to the system default type for destination files,
similarly to the 'restorecon' command. The long form of this
option with a specific context specified, will set the context for
newly created files only. With a specified context, if both
SELinux and SMACK are disabled, a warning is issued.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'mknod': Make block or character special files
'mknod' creates a FIFO, character special file, or block special file
with the specified name. Synopsis:
mknod [OPTION]... NAME TYPE [MAJOR MINOR]
Unlike the phrase "special file type" above, the term "special file"
has a technical meaning on Unix: something that can generate or receive
data. Usually this corresponds to a physical piece of hardware, e.g., a
printer or a disk. (These files are typically created at
system-configuration time.) The 'mknod' command is what creates files
of this type. Such devices can be read either a character at a time or
a "block" (many characters) at a time, hence we say there are "block
special" files and "character special" files.
Due to shell aliases and built-in 'mknod' functions, using an
unadorned 'mknod' interactively or in a script may get you different
functionality than that described here. Invoke it via 'env' (i.e., 'env
mknod ...') to avoid interference from the shell.
The arguments after NAME specify the type of file to make:
'p'
for a FIFO
'b'
for a block special file
'c'
for a character special file
When making a block or character special file, the major and minor
device numbers must be given after the file type. If a major or minor
device number begins with '0x' or '0X', it is interpreted as
hexadecimal; otherwise, if it begins with '0', as octal; otherwise, as
decimal.
The program accepts the following option. Also see *note Common
options::.
'-m MODE'
'--mode=MODE'
Set the mode of created files to MODE, which is symbolic as in
'chmod' and uses 'a=rw' as the point of departure. MODE should
specify only file permission bits. *Note File permissions::.
'-Z'
'--context[=CONTEXT]'
Without a specified CONTEXT, adjust the SELinux security context
according to the system default type for destination files,
similarly to the 'restorecon' command. The long form of this
option with a specific context specified, will set the context for
newly created files only. With a specified context, if both
SELinux and SMACK are disabled, a warning is issued.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'mktemp': Create temporary file or directory
'mktemp' manages the creation of temporary files and directories.
Synopsis:
mktemp [OPTION]... [TEMPLATE]
Safely create a temporary file or directory based on TEMPLATE, and
print its name. If given, TEMPLATE must include at least three
consecutive 'X's in the last component. If omitted, the template
'tmp.XXXXXXXXXX' is used, and option '--tmpdir' is implied. The final
run of 'X's in the TEMPLATE will be replaced by alpha-numeric
characters; thus, on a case-sensitive file system, and with a TEMPLATE
including a run of N instances of 'X', there are '62**N' potential file
names.
Older scripts used to create temporary files by simply joining the
name of the program with the process id ('$$') as a suffix. However,
that naming scheme is easily predictable, and suffers from a race
condition where the attacker can create an appropriately named symbolic
link, such that when the script then opens a handle to what it thought
was an unused file, it is instead modifying an existing file. Using the
same scheme to create a directory is slightly safer, since the 'mkdir'
will fail if the target already exists, but it is still inferior because
it allows for denial of service attacks. Therefore, modern scripts
should use the 'mktemp' command to guarantee that the generated name
will be unpredictable, and that knowledge of the temporary file name
implies that the file was created by the current script and cannot be
modified by other users.
When creating a file, the resulting file has read and write
permissions for the current user, but no permissions for the group or
others; these permissions are reduced if the current umask is more
restrictive.
Here are some examples (although note that if you repeat them, you
will most likely get different file names):
• Create a temporary file in the current directory.
$ mktemp file.XXXX
file.H47c
• Create a temporary file with a known suffix.
$ mktemp --suffix=.txt file-XXXX
file-H08W.txt
$ mktemp file-XXXX-XXXX.txt
file-XXXX-eI9L.txt
• Create a secure fifo relative to the user's choice of 'TMPDIR', but
falling back to the current directory rather than '/tmp'. Note
that 'mktemp' does not create fifos, but can create a secure
directory in which the fifo can live. Exit the shell if the
directory or fifo could not be created.
$ dir=$(mktemp -p "${TMPDIR:-.}" -d dir-XXXX) || exit 1
$ fifo=$dir/fifo
$ mkfifo "$fifo" || { rmdir "$dir"; exit 1; }
• Create and use a temporary file if possible, but ignore failure.
The file will reside in the directory named by 'TMPDIR', if
specified, or else in '/tmp'.
$ file=$(mktemp -q) && {
> # Safe to use $file only within this block. Use quotes,
> # since $TMPDIR, and thus $file, may contain whitespace.
> echo ... > "$file"
> rm "$file"
> }
• Act as a semi-random character generator (it is not fully random,
since it is impacted by the contents of the current directory). To
avoid security holes, do not use the resulting names to create a
file.
$ mktemp -u XXX
Gb9
$ mktemp -u XXX
nzC
The program accepts the following options. Also see *note Common
options::.
'-d'
'--directory'
Create a directory rather than a file. The directory will have
read, write, and search permissions for the current user, but no
permissions for the group or others; these permissions are reduced
if the current umask is more restrictive.
'-q'
'--quiet'
Suppress diagnostics about failure to create a file or directory.
The exit status will still reflect whether a file was created.
'-u'
'--dry-run'
Generate a temporary name that does not name an existing file,
without changing the file system contents. Using the output of
this command to create a new file is inherently unsafe, as there is
a window of time between generating the name and using it where
another process can create an object by the same name.
'-p DIR'
'--tmpdir[=DIR]'
Treat TEMPLATE relative to the directory DIR. If DIR is not
specified (only possible with the long option '--tmpdir') or is the
empty string, use the value of 'TMPDIR' if available, otherwise use
'/tmp'. If this is specified, TEMPLATE must not be absolute.
However, TEMPLATE can still contain slashes, although intermediate
directories must already exist.
'--suffix=SUFFIX'
Append SUFFIX to the TEMPLATE. SUFFIX must not contain slash. If
'--suffix' is specified, TEMPLATE must end in 'X'; if it is not
specified, then an appropriate '--suffix' is inferred by finding
the last 'X' in TEMPLATE. This option exists for use with the
default TEMPLATE and for the creation of a SUFFIX that starts with
'X'.
'-t'
Treat TEMPLATE as a single file relative to the value of 'TMPDIR'
if available, or to the directory specified by '-p', otherwise to
'/tmp'. TEMPLATE must not contain slashes. This option is
deprecated; the use of '-p' without '-t' offers better defaults (by
favoring the command line over 'TMPDIR') and more flexibility (by
allowing intermediate directories).
Exit status:
0 if the file was created,
1 otherwise.
(coreutils)
'mv': Move (rename) files
'mv' moves or renames files (or directories). Synopses:
mv [OPTION]... [-T] SOURCE DEST
mv [OPTION]... SOURCE... DIRECTORY
mv [OPTION]... -t DIRECTORY SOURCE...
• If two file names are given, 'mv' moves the first file to the
second.
• If the '--target-directory' ('-t') option is given, or failing that
if the last file is a directory and the '--no-target-directory'
('-T') option is not given, 'mv' moves each SOURCE file to the
specified directory, using the SOURCEs' names.
'mv' can move any type of file from one file system to another.
Prior to version '4.0' of the fileutils, 'mv' could move only regular
files between file systems. For example, now 'mv' can move an entire
directory hierarchy including special device files from one partition to
another. It first uses some of the same code that's used by 'cp -a' to
copy the requested directories and files, then (assuming the copy
succeeded) it removes the originals. If the copy fails, then the part
that was copied to the destination partition is removed. If you were to
copy three directories from one partition to another and the copy of the
first directory succeeded, but the second didn't, the first would be
left on the destination partition and the second and third would be left
on the original partition.
'mv' always tries to copy extended attributes (xattr), which may
include SELinux context, ACLs or Capabilities. Upon failure all but
'Operation not supported' warnings are output.
If a destination file exists but is normally unwritable, standard
input is a terminal, and the '-f' or '--force' option is not given, 'mv'
prompts the user for whether to replace the file. (You might own the
file, or have write permission on its directory.) If the response is
not affirmative, the file is skipped.
_Warning_: Avoid specifying a source name with a trailing slash, when
it might be a symlink to a directory. Otherwise, 'mv' may do something
very surprising, since its behavior depends on the underlying rename
system call. On a system with a modern Linux-based kernel, it fails
with 'errno=ENOTDIR'. However, on other systems (at least FreeBSD 6.1
and Solaris 10) it silently renames not the symlink but rather the
directory referenced by the symlink. *Note Trailing slashes::.
The program accepts the following options. Also see *note Common
options::.
'-b'
'--backup[=METHOD]'
*Note Backup options::. Make a backup of each file that would
otherwise be overwritten or removed.
'-f'
'--force'
Do not prompt the user before removing a destination file. If you
specify more than one of the '-i', '-f', '-n' options, only the
final one takes effect.
'-i'
'--interactive'
Prompt whether to overwrite each existing destination file,
regardless of its permissions. If the response is not affirmative,
the file is skipped. If you specify more than one of the '-i',
'-f', '-n' options, only the final one takes effect.
'-n'
'--no-clobber'
Do not overwrite an existing file. If you specify more than one of
the '-i', '-f', '-n' options, only the final one takes effect.
This option is mutually exclusive with '-b' or '--backup' option.
'-u'
'--update'
Do not move a non-directory that has an existing destination with
the same or newer modification time. If the move is across file
system boundaries, the comparison is to the source time stamp
truncated to the resolutions of the destination file system and of
the system calls used to update time stamps; this avoids duplicate
work if several 'mv -u' commands are executed with the same source
and destination.
'-v'
'--verbose'
Print the name of each file before moving it.
'--strip-trailing-slashes'
Remove any trailing slashes from each SOURCE argument. *Note
Trailing slashes::.
'-S SUFFIX'
'--suffix=SUFFIX'
Append SUFFIX to each backup file made with '-b'. *Note Backup
options::.
'-t DIRECTORY'
'--target-directory=DIRECTORY'
Specify the destination DIRECTORY. *Note Target directory::.
'-T'
'--no-target-directory'
Do not treat the last operand specially when it is a directory or a
symbolic link to a directory. *Note Target directory::.
'-Z'
'--context'
This option functions similarly to the 'restorecon' command, by
adjusting the SELinux security context according to the system
default type for destination files.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'nice': Run a command with modified niceness
'nice' prints a process's "niceness", or runs a command with modified
niceness. "niceness" affects how favorably the process is scheduled in
the system. Synopsis:
nice [OPTION]... [COMMAND [ARG]...]
If no arguments are given, 'nice' prints the current niceness.
Otherwise, 'nice' runs the given COMMAND with its niceness adjusted. By
default, its niceness is incremented by 10.
Niceness values range at least from −20 (process has high priority
and gets more resources, thus slowing down other processes) through 19
(process has lower priority and runs slowly itself, but has less impact
on the speed of other running processes). Some systems may have a wider
range of niceness values; conversely, other systems may enforce more
restrictive limits. An attempt to set the niceness outside the
supported range is treated as an attempt to use the minimum or maximum
supported value.
A niceness should not be confused with a scheduling priority, which
lets applications determine the order in which threads are scheduled to
run. Unlike a priority, a niceness is merely advice to the scheduler,
which the scheduler is free to ignore. Also, as a point of terminology,
POSIX defines the behavior of 'nice' in terms of a "nice value", which
is the nonnegative difference between a niceness and the minimum
niceness. Though 'nice' conforms to POSIX, its documentation and
diagnostics use the term "niceness" for compatibility with historical
practice.
COMMAND must not be a special built-in utility (*note Special
built-in utilities::).
Due to shell aliases and built-in 'nice' functions, using an
unadorned 'nice' interactively or in a script may get you different
functionality than that described here. Invoke it via 'env' (i.e., 'env
nice ...') to avoid interference from the shell.
Note to change the "niceness" of an existing process, one needs to
use the 'renice' command.
The program accepts the following option. Also see *note Common
options::. Options must precede operands.
'-n ADJUSTMENT'
'--adjustment=ADJUSTMENT'
Add ADJUSTMENT instead of 10 to the command's niceness. If
ADJUSTMENT is negative and you lack appropriate privileges, 'nice'
issues a warning but otherwise acts as if you specified a zero
adjustment.
For compatibility 'nice' also supports an obsolete option syntax
'-ADJUSTMENT'. New scripts should use '-n ADJUSTMENT' instead.
Exit status:
0 if no COMMAND is specified and the niceness is output
125 if 'nice' itself fails
126 if COMMAND is found but cannot be invoked
127 if COMMAND cannot be found
the exit status of COMMAND otherwise
It is sometimes useful to run a non-interactive program with reduced
niceness.
$ nice factor 4611686018427387903
Since 'nice' prints the current niceness, you can invoke it through
itself to demonstrate how it works.
The default behavior is to increase the niceness by '10':
$ nice
0
$ nice nice
10
$ nice -n 10 nice
10
The ADJUSTMENT is relative to the current niceness. In the next
example, the first 'nice' invocation runs the second one with niceness
10, and it in turn runs the final one with a niceness that is 3 more:
$ nice nice -n 3 nice
13
Specifying a niceness larger than the supported range is the same as
specifying the maximum supported value:
$ nice -n 10000000000 nice
19
Only a privileged user may run a process with lower niceness:
$ nice -n -1 nice
nice: cannot set niceness: Permission denied
0
$ sudo nice -n -1 nice
-1
(coreutils)
'nl': Number lines and write files
'nl' writes each FILE ('-' means standard input), or standard input if
none are given, to standard output, with line numbers added to some or
all of the lines. Synopsis:
nl [OPTION]... [FILE]...
'nl' decomposes its input into (logical) pages; by default, the line
number is reset to 1 at the top of each logical page. 'nl' treats all
of the input files as a single document; it does not reset line numbers
or logical pages between files.
A logical page consists of three sections: header, body, and footer.
Any of the sections can be empty. Each can be numbered in a different
style from the others.
The beginnings of the sections of logical pages are indicated in the
input file by a line containing exactly one of these delimiter strings:
'\:\:\:'
start of header;
'\:\:'
start of body;
'\:'
start of footer.
The two characters from which these strings are made can be changed
from '\' and ':' via options (see below), but the pattern and length of
each string cannot be changed.
A section delimiter is replaced by an empty line on output. Any text
that comes before the first section delimiter string in the input file
is considered to be part of a body section, so 'nl' treats a file that
contains no section delimiters as a single body section.
The program accepts the following options. Also see *note Common
options::.
'-b STYLE'
'--body-numbering=STYLE'
Select the numbering style for lines in the body section of each
logical page. When a line is not numbered, the current line number
is not incremented, but the line number separator character is
still prepended to the line. The styles are:
'a'
number all lines,
't'
number only nonempty lines (default for body),
'n'
do not number lines (default for header and footer),
'pBRE'
number only lines that contain a match for the basic regular
expression BRE. *Note Regular Expressions: (grep)Regular
Expressions.
'-d CD'
'--section-delimiter=CD'
Set the section delimiter characters to CD; default is '\:'. If
only C is given, the second remains ':'. (Remember to protect '\'
or other metacharacters from shell expansion with quotes or extra
backslashes.)
'-f STYLE'
'--footer-numbering=STYLE'
Analogous to '--body-numbering'.
'-h STYLE'
'--header-numbering=STYLE'
Analogous to '--body-numbering'.
'-i NUMBER'
'--line-increment=NUMBER'
Increment line numbers by NUMBER (default 1).
'-l NUMBER'
'--join-blank-lines=NUMBER'
Consider NUMBER (default 1) consecutive empty lines to be one
logical line for numbering, and only number the last one. Where
fewer than NUMBER consecutive empty lines occur, do not number
them. An empty line is one that contains no characters, not even
spaces or tabs.
'-n FORMAT'
'--number-format=FORMAT'
Select the line numbering format (default is 'rn'):
'ln'
left justified, no leading zeros;
'rn'
right justified, no leading zeros;
'rz'
right justified, leading zeros.
'-p'
'--no-renumber'
Do not reset the line number at the start of a logical page.
'-s STRING'
'--number-separator=STRING'
Separate the line number from the text line in the output with
STRING (default is the TAB character).
'-v NUMBER'
'--starting-line-number=NUMBER'
Set the initial line number on each logical page to NUMBER (default
1).
'-w NUMBER'
'--number-width=NUMBER'
Use NUMBER characters for line numbers (default 6).
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'nohup': Run a command immune to hangups
'nohup' runs the given COMMAND with hangup signals ignored, so that the
command can continue running in the background after you log out.
Synopsis:
nohup COMMAND [ARG]...
If standard input is a terminal, it is redirected from '/dev/null' so
that terminal sessions do not mistakenly consider the terminal to be
used by the command. This is a GNU extension; programs intended to be
portable to non-GNU hosts should use 'nohup COMMAND [ARG]... </dev/null'
instead.
If standard output is a terminal, the command's standard output is
appended to the file 'nohup.out'; if that cannot be written to, it is
appended to the file '$HOME/nohup.out'; and if that cannot be written
to, the command is not run. Any 'nohup.out' or '$HOME/nohup.out' file
created by 'nohup' is made readable and writable only to the user,
regardless of the current umask settings.
If standard error is a terminal, it is normally redirected to the
same file descriptor as the (possibly-redirected) standard output.
However, if standard output is closed, standard error terminal output is
instead appended to the file 'nohup.out' or '$HOME/nohup.out' as above.
To capture the command's output to a file other than 'nohup.out' you
can redirect it. For example, to capture the output of 'make':
nohup make > make.log
'nohup' does not automatically put the command it runs in the
background; you must do that explicitly, by ending the command line with
an '&'. Also, 'nohup' does not alter the niceness of COMMAND; use
'nice' for that, e.g., 'nohup nice COMMAND'.
COMMAND must not be a special built-in utility (*note Special
built-in utilities::).
The only options are '--help' and '--version'. *Note Common
options::. Options must precede operands.
Exit status:
125 if 'nohup' itself fails, and 'POSIXLY_CORRECT' is not set
126 if COMMAND is found but cannot be invoked
127 if COMMAND cannot be found
the exit status of COMMAND otherwise
If 'POSIXLY_CORRECT' is set, internal failures give status 127
instead of 125.
(coreutils)
'nproc': Print the number of available processors
Print the number of processing units available to the current process,
which may be less than the number of online processors. If this
information is not accessible, then print the number of processors
installed. If the 'OMP_NUM_THREADS' environment variable is set, then
it will determine the returned value. The result is guaranteed to be
greater than zero. Synopsis:
nproc [OPTION]
The program accepts the following options. Also see *note Common
options::.
'--all'
Print the number of installed processors on the system, which may
be greater than the number online or available to the current
process. The 'OMP_NUM_THREADS' environment variable is not honored
in this case.
'--ignore=NUMBER'
If possible, exclude this NUMBER of processing units.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'numfmt': Reformat numbers
'numfmt' reads numbers in various representations and reformats them as
requested. The most common usage is converting numbers to/from _human_
representation (e.g. '4G' ↦ '4,000,000,000').
numfmt [OPTION]... [NUMBER]
'numfmt' converts each NUMBER on the command-line according to the
specified options (see below). If no NUMBERs are given, it reads
numbers from standard input. 'numfmt' can optionally extract numbers
from specific columns, maintaining proper line padding and alignment.
An exit status of zero indicates success, and a nonzero value
indicates failure.
See '--invalid' for additional information regarding exit status.
General options
---------------
The program accepts the following options. Also see *note Common
options::.
'--debug'
Print (to standard error) warning messages about possible erroneous
usage.
'-d D'
'--delimiter=D'
Use the character D as input field separator (default: whitespace).
_Note_: Using non-default delimiter turns off automatic padding.
'--field=N'
Convert the number in input field N (default: 1).
'--format=FORMAT'
Use printf-style floating FORMAT string. The FORMAT string must
contain one '%f' directive, optionally with ''', '-', '0', or width
modifiers. The ''' modifier will enable '--grouping', the '-'
modifier will enable left-aligned '--padding' and the width
modifier will enable right-aligned '--padding'. The '0' width
modifier (without the '-' modifier) will generate leading zeros on
the number, up to the specified width.
'--from=UNIT'
Auto-scales input numbers according to UNIT. See UNITS below. The
default is no scaling, meaning suffixes (e.g. 'M', 'G') will
trigger an error.
'--from-unit=N'
Specify the input unit size (instead of the default 1). Use this
option when the input numbers represent other units (e.g. if the
input number '10' represents 10 units of 512 bytes, use
'--from=unit=512').
'--grouping'
Group digits in output numbers according to the current locale's
grouping rules (e.g _Thousands Separator_ character, commonly '.'
(dot) or ',' comma). This option has no effect in 'POSIX/C'
locale.
'--header[=N]'
Print the first N (default: 1) lines without any conversion.
'--invalid=MODE'
The default action on input errors is to exit immediately with
status code 2. '--invalid='abort'' explicitly specifies this
default mode. With a MODE of 'fail', print a warning for _each_
conversion error, and exit with status 2. With a MODE of 'warn',
exit with status 0, even in the presence of conversion errors, and
with a MODE of 'ignore' do not even print diagnostics.
'--padding=N'
Pad the output numbers to N characters, by adding spaces. If N is
a positive number, numbers will be right-aligned. If N is a
negative number, numbers will be left-aligned. By default, numbers
are automatically aligned based on the input line's width (only
with the default delimiter).
'--round=METHOD'
When converting number representations, round the number according
to METHOD, which can be 'up', 'down', 'from-zero' (the default),
'towards-zero', 'nearest'.
'--suffix=SUFFIX'
Add 'SUFFIX' to the output numbers, and accept optional 'SUFFIX' in
input numbers.
'--to=UNIT'
Auto-scales output numbers according to UNIT. See _Units_ below.
The default is no scaling, meaning all the digits of the number are
printed.
'--to-unit=N'
Specify the output unit size (instead of the default 1). Use this
option when the output numbers represent other units (e.g. to
represent '4,000,000' bytes in blocks of 1KB, use '--to=si
--to=units=1000').
Possible UNITs:
---------------
The following are the possible UNIT options with '--from=UNITS' and
'--to=UNITS':
NONE
No scaling is performed. For input numbers, no suffixes are
accepted, and any trailing characters following the number will
trigger an error. For output numbers, all digits of the numbers
will be printed.
SI
Auto-scale numbers according to the _International System of Units
(SI)_ standard. For input numbers, accept one of the following
suffixes. For output numbers, values larger than 1000 will be
rounded, and printed with one of the following suffixes:
'K' => 1000^1 = 10^3 (Kilo)
'M' => 1000^2 = 10^6 (Mega)
'G' => 1000^3 = 10^9 (Giga)
'T' => 1000^4 = 10^{12} (Tera)
'P' => 1000^5 = 10^{15} (Peta)
'E' => 1000^6 = 10^{18} (Exa)
'Z' => 1000^7 = 10^{21} (Zetta)
'Y' => 1000^8 = 10^{24} (Yotta)
IEC
Auto-scale numbers according to the _International Electronical
Commission (IEC)_ standard. For input numbers, accept one of the
following suffixes. For output numbers, values larger than 1024
will be rounded, and printed with one of the following suffixes:
'K' => 1024^1 = 2^{10} (Kibi)
'M' => 1024^2 = 2^{20} (Mebi)
'G' => 1024^3 = 2^{30} (Gibi)
'T' => 1024^4 = 2^{40} (Tebi)
'P' => 1024^5 = 2^{50} (Pebi)
'E' => 1024^6 = 2^{60} (Exbi)
'Z' => 1024^7 = 2^{70} (Zebi)
'Y' => 1024^8 = 2^{80} (Yobi)
The 'iec' option uses a single letter suffix (e.g. 'G'), which is
not fully standard, as the _iec_ standard recommends a two-letter
symbol (e.g 'Gi') - but in practice, this method common. Compare
with the 'iec-i' option.
IEC-I
Auto-scale numbers according to the _International Electronical
Commission (IEC)_ standard. For input numbers, accept one of the
following suffixes. For output numbers, values larger than 1024
will be rounded, and printed with one of the following suffixes:
'Ki' => 1024^1 = 2^{10} (Kibi)
'Mi' => 1024^2 = 2^{20} (Mebi)
'Gi' => 1024^3 = 2^{30} (Gibi)
'Ti' => 1024^4 = 2^{40} (Tebi)
'Pi' => 1024^5 = 2^{50} (Pebi)
'Ei' => 1024^6 = 2^{60} (Exbi)
'Zi' => 1024^7 = 2^{70} (Zebi)
'Yi' => 1024^8 = 2^{80} (Yobi)
The 'iec-i' option uses a two-letter suffix symbol (e.g. 'Gi'), as
the _iec_ standard recommends, but this is not always common in
practice. Compare with the 'iec' option.
AUTO
'auto' can only be used with '--from'. With this method, numbers
with 'K','M','G','T','P','E','Z','Y' suffixes are interpreted as
_SI_ values, and numbers with 'Ki',
'Mi','Gi','Ti','Pi','Ei','Zi','Yi' suffixes are interpreted as
_IEC_ values.
Examples of using 'numfmt'
--------------------------
Converting a single number from/to _human_ representation:
$ numfmt --to=si 500000
500K
$ numfmt --to=iec 500000
489K
$ numfmt --to=iec-i 500000
489Ki
$ numfmt --from=si 1M
1000000
$ numfmt --from=iec 1M
1048576
# with '--from=auto', M=Mega, Mi=Mebi
$ numfmt --from=auto 1M
1000000
$ numfmt --from=auto 1Mi
1048576
Converting from 'SI' to 'IEC' scales (e.g. when a harddisk capacity
is advertised as '1TB', while checking the drive's capacity gives lower
values):
$ numfmt --from=si --to=iec 1T
932G
Converting a single field from an input file / piped input (these
contrived examples are for demonstration purposes only, as both 'ls' and
'df' support the '--human-readable' option to output sizes in
human-readable format):
# Third field (file size) will be shown in SI representation
$ ls -log | numfmt --field 3 --header --to=si | head -n4
-rw-r--r-- 1 94K Aug 23 2011 ABOUT-NLS
-rw-r--r-- 1 3.7K Jan 7 16:15 AUTHORS
-rw-r--r-- 1 36K Jun 1 2011 COPYING
-rw-r--r-- 1 0 Jan 7 15:15 ChangeLog
# Second field (size) will be shown in IEC representation
$ df --block-size=1 | numfmt --field 2 --header --to=iec | head -n4
File system 1B-blocks Used Available Use% Mounted on
rootfs 132G 104741408 26554036 80% /
tmpfs 794M 7580 804960 1% /run/shm
/dev/sdb1 694G 651424756 46074696 94% /home
Output can be tweaked using '--padding' or '--format':
# Pad to 10 characters, right-aligned
$ du -s * | numfmt --to=si --padding=10
2.5K config.log
108 config.status
1.7K configure
20 configure.ac
# Pad to 10 characters, left-aligned
$ du -s * | numfmt --to=si --padding=-10
2.5K config.log
108 config.status
1.7K configure
20 configure.ac
# Pad to 10 characters, left-aligned, using 'format'
$ du -s * | numfmt --to=si --format="%10f"
2.5K config.log
108 config.status
1.7K configure
20 configure.ac
# Pad to 10 characters, left-aligned, using 'format'
$ du -s * | numfmt --to=si --padding="%-10f"
2.5K config.log
108 config.status
1.7K configure
20 configure.ac
With locales that support grouping digits, using '--grouping' or
'--format' enables grouping. In 'POSIX' locale, grouping is silently
ignored:
$ LC_ALL=C numfmt --from=iec --grouping 2G
2147483648
$ LC_ALL=en_US.utf8 numfmt --from=iec --grouping 2G
2,147,483,648
$ LC_ALL=ta_IN numfmt --from=iec --grouping 2G
2,14,74,83,648
$ LC_ALL=C ./src/numfmt --from=iec --format="==%'15f==" 2G
== 2147483648==
$ LC_ALL=en_US.utf8 ./src/numfmt --from=iec --format="==%'15f==" 2G
== 2,147,483,648==
$ LC_ALL=en_US.utf8 ./src/numfmt --from=iec --format="==%'-15f==" 2G
==2,147,483,648 ==
$ LC_ALL=ta_IN ./src/numfmt --from=iec --format="==%'15f==" 2G
== 2,14,74,83,648==
(coreutils)
'od': Write files in octal or other formats
'od' writes an unambiguous representation of each FILE ('-' means
standard input), or standard input if none are given. Synopses:
od [OPTION]... [FILE]...
od [-abcdfilosx]... [FILE] [[+]OFFSET[.][b]]
od [OPTION]... --traditional [FILE] [[+]OFFSET[.][b] [[+]LABEL[.][b]]]
Each line of output consists of the offset in the input, followed by
groups of data from the file. By default, 'od' prints the offset in
octal, and each group of file data is a C 'short int''s worth of input
printed as a single octal number.
If OFFSET is given, it specifies how many input bytes to skip before
formatting and writing. By default, it is interpreted as an octal
number, but the optional trailing decimal point causes it to be
interpreted as decimal. If no decimal is specified and the offset
begins with '0x' or '0X' it is interpreted as a hexadecimal number. If
there is a trailing 'b', the number of bytes skipped will be OFFSET
multiplied by 512.
If a command is of both the first and second forms, the second form
is assumed if the last operand begins with '+' or (if there are two
operands) a digit. For example, in 'od foo 10' and 'od +10' the '10' is
an offset, whereas in 'od 10' the '10' is a file name.
The program accepts the following options. Also see *note Common
options::.
'-A RADIX'
'--address-radix=RADIX'
Select the base in which file offsets are printed. RADIX can be
one of the following:
'd'
decimal;
'o'
octal;
'x'
hexadecimal;
'n'
none (do not print offsets).
The default is octal.
'--endian=ORDER'
Reorder input bytes, to handle inputs with differing byte orders,
or to provide consistent output independent of the endian
convention of the current system. Swapping is performed according
to the specified '--type' size and endian ORDER, which can be
'little' or 'big'.
'-j BYTES'
'--skip-bytes=BYTES'
Skip BYTES input bytes before formatting and writing. If BYTES
begins with '0x' or '0X', it is interpreted in hexadecimal;
otherwise, if it begins with '0', in octal; otherwise, in decimal.
BYTES may be, or may be an integer optionally followed by, one of
the following multiplicative suffixes:
'b' => 512 ("blocks")
'KB' => 1000 (KiloBytes)
'K' => 1024 (KibiBytes)
'MB' => 1000*1000 (MegaBytes)
'M' => 1024*1024 (MebiBytes)
'GB' => 1000*1000*1000 (GigaBytes)
'G' => 1024*1024*1024 (GibiBytes)
and so on for 'T', 'P', 'E', 'Z', and 'Y'.
'-N BYTES'
'--read-bytes=BYTES'
Output at most BYTES bytes of the input. Prefixes and suffixes on
'bytes' are interpreted as for the '-j' option.
'-S BYTES'
'--strings[=BYTES]'
Instead of the normal output, output only "string constants": at
least BYTES consecutive ASCII graphic characters, followed by a
zero byte (ASCII NUL). Prefixes and suffixes on BYTES are
interpreted as for the '-j' option.
If BYTES is omitted with '--strings', the default is 3.
'-t TYPE'
'--format=TYPE'
Select the format in which to output the file data. TYPE is a
string of one or more of the below type indicator characters. If
you include more than one type indicator character in a single TYPE
string, or use this option more than once, 'od' writes one copy of
each output line using each of the data types that you specified,
in the order that you specified.
Adding a trailing "z" to any type specification appends a display
of the single byte character representation of the printable
characters to the output line generated by the type specification.
'a'
named character, ignoring high-order bit
'c'
printable single byte character, C backslash escape or a 3
digit octal sequence
'd'
signed decimal
'f'
floating point (*note Floating point::)
'o'
octal
'u'
unsigned decimal
'x'
hexadecimal
The type 'a' outputs things like 'sp' for space, 'nl' for newline,
and 'nul' for a zero byte. Only the least significant seven bits
of each byte is used; the high-order bit is ignored. Type 'c'
outputs ' ', '\n', and '\0', respectively.
Except for types 'a' and 'c', you can specify the number of bytes
to use in interpreting each number in the given data type by
following the type indicator character with a decimal integer.
Alternately, you can specify the size of one of the C compiler's
built-in data types by following the type indicator character with
one of the following characters. For integers ('d', 'o', 'u',
'x'):
'C'
char
'S'
short
'I'
int
'L'
long
For floating point ('f'):
F
float
D
double
L
long double
'-v'
'--output-duplicates'
Output consecutive lines that are identical. By default, when two
or more consecutive output lines would be identical, 'od' outputs
only the first line, and puts just an asterisk on the following
line to indicate the elision.
'-w[N]'
'--width[=N]'
Dump 'n' input bytes per output line. This must be a multiple of
the least common multiple of the sizes associated with the
specified output types.
If this option is not given at all, the default is 16. If N is
omitted, the default is 32.
The next several options are shorthands for format specifications.
GNU 'od' accepts any combination of shorthands and format specification
options. These options accumulate.
'-a'
Output as named characters. Equivalent to '-t a'.
'-b'
Output as octal bytes. Equivalent to '-t o1'.
'-c'
Output as printable single byte characters, C backslash escapes or
3 digit octal sequences. Equivalent to '-t c'.
'-d'
Output as unsigned decimal two-byte units. Equivalent to '-t u2'.
'-f'
Output as floats. Equivalent to '-t fF'.
'-i'
Output as decimal ints. Equivalent to '-t dI'.
'-l'
Output as decimal long ints. Equivalent to '-t dL'.
'-o'
Output as octal two-byte units. Equivalent to '-t o2'.
'-s'
Output as decimal two-byte units. Equivalent to '-t d2'.
'-x'
Output as hexadecimal two-byte units. Equivalent to '-t x2'.
'--traditional'
Recognize the non-option label argument that traditional 'od'
accepted. The following syntax:
od --traditional [FILE] [[+]OFFSET[.][b] [[+]LABEL[.][b]]]
can be used to specify at most one file and optional arguments
specifying an offset and a pseudo-start address, LABEL. The LABEL
argument is interpreted just like OFFSET, but it specifies an
initial pseudo-address. The pseudo-addresses are displayed in
parentheses following any normal address.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'paste': Merge lines of files
'paste' writes to standard output lines consisting of sequentially
corresponding lines of each given file, separated by a TAB character.
Standard input is used for a file name of '-' or if no input files are
given.
Synopsis:
paste [OPTION]... [FILE]...
For example, with:
$ cat num2
1
2
$ cat let3
a
b
c
Take lines sequentially from each file:
$ paste num2 let3
1 a
2 b
c
Duplicate lines from a file:
$ paste num2 let3 num2
1 a 1
2 b 2
c
Intermix lines from stdin:
$ paste - let3 - < num2
1 a 2
b
c
Join consecutive lines with a space:
$ seq 4 | paste -d ' ' - -
1 2
3 4
The program accepts the following options. Also see *note Common
options::.
'-s'
'--serial'
Paste the lines of one file at a time rather than one line from
each file. Using the above example data:
$ paste -s num2 let3
1 2
a b c
'-d DELIM-LIST'
'--delimiters=DELIM-LIST'
Consecutively use the characters in DELIM-LIST instead of TAB to
separate merged lines. When DELIM-LIST is exhausted, start again
at its beginning. Using the above example data:
$ paste -d '%_' num2 let3 num2
1%a_1
2%b_2
%c_
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'pathchk': Check file name validity and portability
'pathchk' checks validity and portability of file names. Synopsis:
pathchk [OPTION]... NAME...
For each NAME, 'pathchk' prints an error message if any of these
conditions is true:
1. One of the existing directories in NAME does not have search
(execute) permission,
2. The length of NAME is larger than the maximum supported by the
operating system.
3. The length of one component of NAME is longer than its file
system's maximum.
A nonexistent NAME is not an error, so long a file with that name
could be created under the above conditions.
The program accepts the following options. Also see *note Common
options::. Options must precede operands.
'-p'
Instead of performing checks based on the underlying file system,
print an error message if any of these conditions is true:
1. A file name is empty.
2. A file name contains a character outside the POSIX portable
file name character set, namely, the ASCII letters and digits,
'.', '_', '-', and '/'.
3. The length of a file name or one of its components exceeds the
POSIX minimum limits for portability.
'-P'
Print an error message if a file name is empty, or if it contains a
component that begins with '-'.
'--portability'
Print an error message if a file name is not portable to all POSIX
hosts. This option is equivalent to '-p -P'.
Exit status:
0 if all specified file names passed all checks,
1 otherwise.
(builtin command)
popd: popd [-n] [+N | -N]
Remove directories from stack.
Removes entries from the directory stack. With no arguments, removes
the top directory from the stack, and changes to the new top directory.
Options:
-n Suppresses the normal change of directory when removing
directories from the stack, so only the stack is manipulated.
Arguments:
+N Removes the Nth entry counting from the left of the list
shown by 'dirs', starting with zero. For example: 'popd +0'
removes the first directory, 'popd +1' the second.
-N Removes the Nth entry counting from the right of the list
shown by 'dirs', starting with zero. For example: 'popd -0'
removes the last directory, 'popd -1' the next to last.
The 'dirs' builtin displays the directory stack.
Exit Status:
Returns success unless an invalid argument is supplied or the directory
change fails.
(coreutils)
'pr': Paginate or columnate files for printing
'pr' writes each FILE ('-' means standard input), or standard input if
none are given, to standard output, paginating and optionally outputting
in multicolumn format; optionally merges all FILEs, printing all in
parallel, one per column. Synopsis:
pr [OPTION]... [FILE]...
By default, a 5-line header is printed at each page: two blank lines;
a line with the date, the file name, and the page count; and two more
blank lines. A footer of five blank lines is also printed. The default
PAGE_LENGTH is 66 lines. The default number of text lines is therefore
56. The text line of the header takes the form 'DATE STRING PAGE', with
spaces inserted around STRING so that the line takes up the full
PAGE_WIDTH. Here, DATE is the date (see the '-D' or '--date-format'
option for details), STRING is the centered header string, and PAGE
identifies the page number. The 'LC_MESSAGES' locale category affects
the spelling of PAGE; in the default C locale, it is 'Page NUMBER' where
NUMBER is the decimal page number.
Form feeds in the input cause page breaks in the output. Multiple
form feeds produce empty pages.
Columns are of equal width, separated by an optional string (default
is 'space'). For multicolumn output, lines will always be truncated to
PAGE_WIDTH (default 72), unless you use the '-J' option. For single
column output no line truncation occurs by default. Use '-W' option to
truncate lines in that case.
The program accepts the following options. Also see *note Common
options::.
'+FIRST_PAGE[:LAST_PAGE]'
'--pages=FIRST_PAGE[:LAST_PAGE]'
Begin printing with page FIRST_PAGE and stop with LAST_PAGE.
Missing ':LAST_PAGE' implies end of file. While estimating the
number of skipped pages each form feed in the input file results in
a new page. Page counting with and without '+FIRST_PAGE' is
identical. By default, counting starts with the first page of
input file (not first page printed). Line numbering may be altered
by '-N' option.
'-COLUMN'
'--columns=COLUMN'
With each single FILE, produce COLUMN columns of output (default is
1) and print columns down, unless '-a' is used. The column width
is automatically decreased as COLUMN increases; unless you use the
'-W/-w' option to increase PAGE_WIDTH as well. This option might
well cause some lines to be truncated. The number of lines in the
columns on each page are balanced. The options '-e' and '-i' are
on for multiple text-column output. Together with '-J' option
column alignment and line truncation is turned off. Lines of full
length are joined in a free field format and '-S' option may set
field separators. '-COLUMN' may not be used with '-m' option.
'-a'
'--across'
With each single FILE, print columns across rather than down. The
'-COLUMN' option must be given with COLUMN greater than one. If a
line is too long to fit in a column, it is truncated.
'-c'
'--show-control-chars'
Print control characters using hat notation (e.g., '^G'); print
other nonprinting characters in octal backslash notation. By
default, nonprinting characters are not changed.
'-d'
'--double-space'
Double space the output.
'-D FORMAT'
'--date-format=FORMAT'
Format header dates using FORMAT, using the same conventions as for
the command 'date +FORMAT'. *Note date invocation::. Except for
directives, which start with '%', characters in FORMAT are printed
unchanged. You can use this option to specify an arbitrary string
in place of the header date, e.g., '--date-format="Monday
morning"'.
The default date format is '%Y-%m-%d %H:%M' (for example,
'2001-12-04 23:59'); but if the 'POSIXLY_CORRECT' environment
variable is set and the 'LC_TIME' locale category specifies the
POSIX locale, the default is '%b %e %H:%M %Y' (for example, 'Dec 4
23:59 2001'.
Time stamps are listed according to the time zone rules specified
by the 'TZ' environment variable, or by the system default rules if
'TZ' is not set. *Note Specifying the Time Zone with 'TZ':
(libc)TZ Variable.
'-e[IN-TABCHAR[IN-TABWIDTH]]'
'--expand-tabs[=IN-TABCHAR[IN-TABWIDTH]]'
Expand TABs to spaces on input. Optional argument IN-TABCHAR is
the input tab character (default is the TAB character). Second
optional argument IN-TABWIDTH is the input tab character's width
(default is 8).
'-f'
'-F'
'--form-feed'
Use a form feed instead of newlines to separate output pages. This
does not alter the default page length of 66 lines.
'-h HEADER'
'--header=HEADER'
Replace the file name in the header with the centered string
HEADER. When using the shell, HEADER should be quoted and should
be separated from '-h' by a space.
'-i[OUT-TABCHAR[OUT-TABWIDTH]]'
'--output-tabs[=OUT-TABCHAR[OUT-TABWIDTH]]'
Replace spaces with TABs on output. Optional argument OUT-TABCHAR
is the output tab character (default is the TAB character). Second
optional argument OUT-TABWIDTH is the output tab character's width
(default is 8).
'-J'
'--join-lines'
Merge lines of full length. Used together with the column options
'-COLUMN', '-a -COLUMN' or '-m'. Turns off '-W/-w' line
truncation; no column alignment used; may be used with
'--sep-string[=STRING]'. '-J' has been introduced (together with
'-W' and '--sep-string') to disentangle the old (POSIX-compliant)
options '-w' and '-s' along with the three column options.
'-l PAGE_LENGTH'
'--length=PAGE_LENGTH'
Set the page length to PAGE_LENGTH (default 66) lines, including
the lines of the header [and the footer]. If PAGE_LENGTH is less
than or equal to 10, the header and footer are omitted, as if the
'-t' option had been given.
'-m'
'--merge'
Merge and print all FILEs in parallel, one in each column. If a
line is too long to fit in a column, it is truncated, unless the
'-J' option is used. '--sep-string[=STRING]' may be used. Empty
pages in some FILEs (form feeds set) produce empty columns, still
marked by STRING. The result is a continuous line numbering and
column marking throughout the whole merged file. Completely empty
merged pages show no separators or line numbers. The default
header becomes 'DATE PAGE' with spaces inserted in the middle; this
may be used with the '-h' or '--header' option to fill up the
middle blank part.
'-n[NUMBER-SEPARATOR[DIGITS]]'
'--number-lines[=NUMBER-SEPARATOR[DIGITS]]'
Provide DIGITS digit line numbering (default for DIGITS is 5).
With multicolumn output the number occupies the first DIGITS column
positions of each text column or only each line of '-m' output.
With single column output the number precedes each line just as
'-m' does. Default counting of the line numbers starts with the
first line of the input file (not the first line printed, compare
the '--page' option and '-N' option). Optional argument
NUMBER-SEPARATOR is the character appended to the line number to
separate it from the text followed. The default separator is the
TAB character. In a strict sense a TAB is always printed with
single column output only. The TAB width varies with the TAB
position, e.g., with the left MARGIN specified by '-o' option.
With multicolumn output priority is given to 'equal width of output
columns' (a POSIX specification). The TAB width is fixed to the
value of the first column and does not change with different values
of left MARGIN. That means a fixed number of spaces is always
printed in the place of the NUMBER-SEPARATOR TAB. The tabification
depends upon the output position.
'-N LINE_NUMBER'
'--first-line-number=LINE_NUMBER'
Start line counting with the number LINE_NUMBER at first line of
first page printed (in most cases not the first line of the input
file).
'-o MARGIN'
'--indent=MARGIN'
Indent each line with a margin MARGIN spaces wide (default is
zero). The total page width is the size of the margin plus the
PAGE_WIDTH set with the '-W/-w' option. A limited overflow may
occur with numbered single column output (compare '-n' option).
'-r'
'--no-file-warnings'
Do not print a warning message when an argument FILE cannot be
opened. (The exit status will still be nonzero, however.)
'-s[CHAR]'
'--separator[=CHAR]'
Separate columns by a single character CHAR. The default for CHAR
is the TAB character without '-w' and 'no character' with '-w'.
Without '-s' the default separator 'space' is set. '-s[char]'
turns off line truncation of all three column options
('-COLUMN'|'-a -COLUMN'|'-m') unless '-w' is set. This is a
POSIX-compliant formulation.
'-S[STRING]'
'--sep-string[=STRING]'
Use STRING to separate output columns. The '-S' option doesn't
affect the '-W/-w' option, unlike the '-s' option which does. It
does not affect line truncation or column alignment. Without '-S',
and with '-J', 'pr' uses the default output separator, TAB.
Without '-S' or '-J', 'pr' uses a 'space' (same as '-S" "'). If no
'STRING' argument is specified, '""' is assumed.
'-t'
'--omit-header'
Do not print the usual header [and footer] on each page, and do not
fill out the bottom of pages (with blank lines or a form feed). No
page structure is produced, but form feeds set in the input files
are retained. The predefined pagination is not changed. '-t' or
'-T' may be useful together with other options; e.g.: '-t -e4',
expand TAB characters in the input file to 4 spaces but don't make
any other changes. Use of '-t' overrides '-h'.
'-T'
'--omit-pagination'
Do not print header [and footer]. In addition eliminate all form
feeds set in the input files.
'-v'
'--show-nonprinting'
Print nonprinting characters in octal backslash notation.
'-w PAGE_WIDTH'
'--width=PAGE_WIDTH'
Set page width to PAGE_WIDTH characters for multiple text-column
output only (default for PAGE_WIDTH is 72). The specified
PAGE_WIDTH is rounded down so that columns have equal width.
'-s[CHAR]' turns off the default page width and any line truncation
and column alignment. Lines of full length are merged, regardless
of the column options set. No PAGE_WIDTH setting is possible with
single column output. A POSIX-compliant formulation.
'-W PAGE_WIDTH'
'--page_width=PAGE_WIDTH'
Set the page width to PAGE_WIDTH characters, honored with and
without a column option. With a column option, the specified
PAGE_WIDTH is rounded down so that columns have equal width. Text
lines are truncated, unless '-J' is used. Together with one of the
three column options ('-COLUMN', '-a -COLUMN' or '-m') column
alignment is always used. The separator options '-S' or '-s' don't
disable the '-W' option. Default is 72 characters. Without '-W
PAGE_WIDTH' and without any of the column options NO line
truncation is used (defined to keep downward compatibility and to
meet most frequent tasks). That's equivalent to '-W 72 -J'. The
header line is never truncated.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'printenv': Print all or some environment variables
'printenv' prints environment variable values. Synopsis:
printenv [OPTION] [VARIABLE]...
If no VARIABLEs are specified, 'printenv' prints the value of every
environment variable. Otherwise, it prints the value of each VARIABLE
that is set, and nothing for those that are not set.
The program accepts the following option. Also see *note Common
options::.
'-0'
'--null'
Output a zero byte (ASCII NUL) at the end of each line, rather than
a newline. This option enables other programs to parse the output
even when that output would contain data with embedded newlines.
Exit status:
0 if all variables specified were found
1 if at least one specified variable was not found
2 if a write error occurred
(coreutils)
'printf': Format and print data
'printf' does formatted printing of text. Synopsis:
printf FORMAT [ARGUMENT]...
'printf' prints the FORMAT string, interpreting '%' directives and
'\' escapes to format numeric and string arguments in a way that is
mostly similar to the C 'printf' function. *Note 'printf' format
directives: (libc)Output Conversion Syntax, for details. The
differences are listed below.
Due to shell aliases and built-in 'printf' functions, using an
unadorned 'printf' interactively or in a script may get you different
functionality than that described here. Invoke it via 'env' (i.e., 'env
printf ...') to avoid interference from the shell.
• The FORMAT argument is reused as necessary to convert all the given
ARGUMENTs. For example, the command 'printf %s a b' outputs 'ab'.
• Missing ARGUMENTs are treated as null strings or as zeros,
depending on whether the context expects a string or a number. For
example, the command 'printf %sx%d' prints 'x0'.
• An additional escape, '\c', causes 'printf' to produce no further
output. For example, the command 'printf 'A%sC\cD%sF' B E' prints
'ABC'.
• The hexadecimal escape sequence '\xHH' has at most two digits, as
opposed to C where it can have an unlimited number of digits. For
example, the command 'printf '\x07e'' prints two bytes, whereas the
C statement 'printf ("\x07e")' prints just one.
• 'printf' has an additional directive, '%b', which prints its
argument string with '\' escapes interpreted in the same way as in
the FORMAT string, except that octal escapes are of the form
'\0OOO' where OOO is 0 to 3 octal digits. If '\OOO' is nine-bit
value, ignore the ninth bit. If a precision is also given, it
limits the number of bytes printed from the converted string.
• Numeric arguments must be single C constants, possibly with leading
'+' or '-'. For example, 'printf %.4d -3' outputs '-0003'.
• If the leading character of a numeric argument is '"' or ''' then
its value is the numeric value of the immediately following
character. Any remaining characters are silently ignored if the
'POSIXLY_CORRECT' environment variable is set; otherwise, a warning
is printed. For example, 'printf "%d" "'a"' outputs '97' on hosts
that use the ASCII character set, since 'a' has the numeric value
97 in ASCII.
A floating-point argument must use a period before any fractional
digits, but is printed according to the 'LC_NUMERIC' category of the
current locale. For example, in a locale whose radix character is a
comma, the command 'printf %g 3.14' outputs '3,14' whereas the command
'printf %g 3,14' is an error. *Note Floating point::.
'printf' interprets '\OOO' in FORMAT as an octal number (if OOO is 1
to 3 octal digits) specifying a byte to print, and '\xHH' as a
hexadecimal number (if HH is 1 to 2 hex digits) specifying a character
to print. Note however that when '\OOO' specifies a number larger than
255, 'printf' ignores the ninth bit. For example, 'printf '\400'' is
equivalent to 'printf '\0''.
'printf' interprets two character syntaxes introduced in ISO C 99:
'\u' for 16-bit Unicode (ISO/IEC 10646) characters, specified as four
hexadecimal digits HHHH, and '\U' for 32-bit Unicode characters,
specified as eight hexadecimal digits HHHHHHHH. 'printf' outputs the
Unicode characters according to the 'LC_CTYPE' locale. Unicode
characters in the ranges U+0000...U+009F, U+D800...U+DFFF cannot be
specified by this syntax, except for U+0024 ($), U+0040 (@), and U+0060
(`).
The processing of '\u' and '\U' requires a full-featured 'iconv'
facility. It is activated on systems with glibc 2.2 (or newer), or when
'libiconv' is installed prior to this package. Otherwise '\u' and '\U'
will print as-is.
The only options are a lone '--help' or '--version'. *Note Common
options::. Options must precede operands.
The Unicode character syntaxes are useful for writing strings in a
locale independent way. For example, a string containing the Euro
currency symbol
$ env printf '\u20AC 14.95'
will be output correctly in all locales supporting the Euro symbol
(ISO-8859-15, UTF-8, and others). Similarly, a Chinese string
$ env printf '\u4e2d\u6587'
will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8,
etc).
Note that in these examples, the 'printf' command has been invoked
via 'env' to ensure that we run the program found via your shell's
search path, and not a shell alias or a built-in function.
For larger strings, you don't need to look up the hexadecimal code
values of each character one by one. ASCII characters mixed with \u
escape sequences is also known as the JAVA source file encoding. You
can use GNU recode 3.5c (or newer) to convert strings to this encoding.
Here is how to convert a piece of text into a shell script which will
output this text in a locale-independent way:
$ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
'\u4e2d\u6587\n' > sample.txt
$ recode BIG5..JAVA < sample.txt \
| sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
> sample.sh
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'printf': Format and print data
'printf' does formatted printing of text. Synopsis:
printf FORMAT [ARGUMENT]...
'printf' prints the FORMAT string, interpreting '%' directives and
'\' escapes to format numeric and string arguments in a way that is
mostly similar to the C 'printf' function. *Note 'printf' format
directives: (libc)Output Conversion Syntax, for details. The
differences are listed below.
Due to shell aliases and built-in 'printf' functions, using an
unadorned 'printf' interactively or in a script may get you different
functionality than that described here. Invoke it via 'env' (i.e., 'env
printf ...') to avoid interference from the shell.
• The FORMAT argument is reused as necessary to convert all the given
ARGUMENTs. For example, the command 'printf %s a b' outputs 'ab'.
• Missing ARGUMENTs are treated as null strings or as zeros,
depending on whether the context expects a string or a number. For
example, the command 'printf %sx%d' prints 'x0'.
• An additional escape, '\c', causes 'printf' to produce no further
output. For example, the command 'printf 'A%sC\cD%sF' B E' prints
'ABC'.
• The hexadecimal escape sequence '\xHH' has at most two digits, as
opposed to C where it can have an unlimited number of digits. For
example, the command 'printf '\x07e'' prints two bytes, whereas the
C statement 'printf ("\x07e")' prints just one.
• 'printf' has an additional directive, '%b', which prints its
argument string with '\' escapes interpreted in the same way as in
the FORMAT string, except that octal escapes are of the form
'\0OOO' where OOO is 0 to 3 octal digits. If '\OOO' is nine-bit
value, ignore the ninth bit. If a precision is also given, it
limits the number of bytes printed from the converted string.
• Numeric arguments must be single C constants, possibly with leading
'+' or '-'. For example, 'printf %.4d -3' outputs '-0003'.
• If the leading character of a numeric argument is '"' or ''' then
its value is the numeric value of the immediately following
character. Any remaining characters are silently ignored if the
'POSIXLY_CORRECT' environment variable is set; otherwise, a warning
is printed. For example, 'printf "%d" "'a"' outputs '97' on hosts
that use the ASCII character set, since 'a' has the numeric value
97 in ASCII.
A floating-point argument must use a period before any fractional
digits, but is printed according to the 'LC_NUMERIC' category of the
current locale. For example, in a locale whose radix character is a
comma, the command 'printf %g 3.14' outputs '3,14' whereas the command
'printf %g 3,14' is an error. *Note Floating point::.
'printf' interprets '\OOO' in FORMAT as an octal number (if OOO is 1
to 3 octal digits) specifying a byte to print, and '\xHH' as a
hexadecimal number (if HH is 1 to 2 hex digits) specifying a character
to print. Note however that when '\OOO' specifies a number larger than
255, 'printf' ignores the ninth bit. For example, 'printf '\400'' is
equivalent to 'printf '\0''.
'printf' interprets two character syntaxes introduced in ISO C 99:
'\u' for 16-bit Unicode (ISO/IEC 10646) characters, specified as four
hexadecimal digits HHHH, and '\U' for 32-bit Unicode characters,
specified as eight hexadecimal digits HHHHHHHH. 'printf' outputs the
Unicode characters according to the 'LC_CTYPE' locale. Unicode
characters in the ranges U+0000...U+009F, U+D800...U+DFFF cannot be
specified by this syntax, except for U+0024 ($), U+0040 (@), and U+0060
()̀.
The processing of '\u' and '\U' requires a full-featured 'iconv'
facility. It is activated on systems with glibc 2.2 (or newer), or when
'libiconv' is installed prior to this package. Otherwise '\u' and '\U'
will print as-is.
The only options are a lone '--help' or '--version'. *Note Common
options::. Options must precede operands.
The Unicode character syntaxes are useful for writing strings in a
locale independent way. For example, a string containing the Euro
currency symbol
$ env printf '\u20AC 14.95'
will be output correctly in all locales supporting the Euro symbol
(ISO-8859-15, UTF-8, and others). Similarly, a Chinese string
$ env printf '\u4e2d\u6587'
will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8,
etc).
Note that in these examples, the 'printf' command has been invoked
via 'env' to ensure that we run the program found via your shell's
search path, and not a shell alias or a built-in function.
For larger strings, you don't need to look up the hexadecimal code
values of each character one by one. ASCII characters mixed with \u
escape sequences is also known as the JAVA source file encoding. You
can use GNU recode 3.5c (or newer) to convert strings to this encoding.
Here is how to convert a piece of text into a shell script which will
output this text in a locale-independent way:
$ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
'\u4e2d\u6587\n' > sample.txt
$ recode BIG5..JAVA < sample.txt \
| sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
> sample.sh
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'ptx': Produce permuted indexes
'ptx' reads a text file and essentially produces a permuted index, with
each keyword in its context. The calling sketch is either one of:
ptx [OPTION ...] [FILE ...]
ptx -G [OPTION ...] [INPUT [OUTPUT]]
The '-G' (or its equivalent: '--traditional') option disables all GNU
extensions and reverts to traditional mode, thus introducing some
limitations and changing several of the program's default option values.
When '-G' is not specified, GNU extensions are always enabled. GNU
extensions to 'ptx' are documented wherever appropriate in this
document. *Note Compatibility in ptx::, for the full list.
Individual options are explained in the following sections.
When GNU extensions are enabled, there may be zero, one or several
FILEs after the options. If there is no FILE, the program reads the
standard input. If there is one or several FILEs, they give the name of
input files which are all read in turn, as if all the input files were
concatenated. However, there is a full contextual break between each
file and, when automatic referencing is requested, file names and line
numbers refer to individual text input files. In all cases, the program
outputs the permuted index to the standard output.
When GNU extensions are _not_ enabled, that is, when the program
operates in traditional mode, there may be zero, one or two parameters
besides the options. If there are no parameters, the program reads the
standard input and outputs the permuted index to the standard output.
If there is only one parameter, it names the text INPUT to be read
instead of the standard input. If two parameters are given, they give
respectively the name of the INPUT file to read and the name of the
OUTPUT file to produce. _Be very careful_ to note that, in this case,
the contents of file given by the second parameter is destroyed. This
behavior is dictated by System V 'ptx' compatibility; GNU Standards
normally discourage output parameters not introduced by an option.
Note that for _any_ file named as the value of an option or as an
input text file, a single dash '-' may be used, in which case standard
input is assumed. However, it would not make sense to use this
convention more than once per program invocation.
* Menu:
* General options in ptx:: Options which affect general program behavior.
* Charset selection in ptx:: Underlying character set considerations.
* Input processing in ptx:: Input fields, contexts, and keyword selection.
* Output formatting in ptx:: Types of output format, and sizing the fields.
* Compatibility in ptx::
General options
---------------
'-G'
'--traditional'
As already explained, this option disables all GNU extensions to
'ptx' and switches to traditional mode.
'--help'
Print a short help on standard output, then exit without further
processing.
'--version'
Print the program version on standard output, then exit without
further processing.
An exit status of zero indicates success, and a nonzero value
indicates failure.
Charset selection
-----------------
As it is set up now, the program assumes that the input file is coded
using 8-bit ISO 8859-1 code, also known as Latin-1 character set,
_unless_ it is compiled for MS-DOS, in which case it uses the character
set of the IBM-PC. (GNU 'ptx' is not known to work on smaller MS-DOS
machines anymore.) Compared to 7-bit ASCII, the set of characters which
are letters is different; this alters the behavior of regular expression
matching. Thus, the default regular expression for a keyword allows
foreign or diacriticized letters. Keyword sorting, however, is still
crude; it obeys the underlying character set ordering quite blindly.
'-f'
'--ignore-case'
Fold lower case letters to upper case for sorting.
Word selection and input processing
-----------------------------------
'-b FILE'
'--break-file=FILE'
This option provides an alternative (to '-W') method of describing
which characters make up words. It introduces the name of a file
which contains a list of characters which can_not_ be part of one
word; this file is called the "Break file". Any character which is
not part of the Break file is a word constituent. If both options
'-b' and '-W' are specified, then '-W' has precedence and '-b' is
ignored.
When GNU extensions are enabled, the only way to avoid newline as a
break character is to write all the break characters in the file
with no newline at all, not even at the end of the file. When GNU
extensions are disabled, spaces, tabs and newlines are always
considered as break characters even if not included in the Break
file.
'-i FILE'
'--ignore-file=FILE'
The file associated with this option contains a list of words which
will never be taken as keywords in concordance output. It is
called the "Ignore file". The file contains exactly one word in
each line; the end of line separation of words is not subject to
the value of the '-S' option.
'-o FILE'
'--only-file=FILE'
The file associated with this option contains a list of words which
will be retained in concordance output; any word not mentioned in
this file is ignored. The file is called the "Only file". The
file contains exactly one word in each line; the end of line
separation of words is not subject to the value of the '-S' option.
There is no default for the Only file. When both an Only file and
an Ignore file are specified, a word is considered a keyword only
if it is listed in the Only file and not in the Ignore file.
'-r'
'--references'
On each input line, the leading sequence of non-white space
characters will be taken to be a reference that has the purpose of
identifying this input line in the resulting permuted index. *Note
Output formatting in ptx::, for more information about reference
production. Using this option changes the default value for option
'-S'.
Using this option, the program does not try very hard to remove
references from contexts in output, but it succeeds in doing so
_when_ the context ends exactly at the newline. If option '-r' is
used with '-S' default value, or when GNU extensions are disabled,
this condition is always met and references are completely excluded
from the output contexts.
'-S REGEXP'
'--sentence-regexp=REGEXP'
This option selects which regular expression will describe the end
of a line or the end of a sentence. In fact, this regular
expression is not the only distinction between end of lines or end
of sentences, and input line boundaries have no special
significance outside this option. By default, when GNU extensions
are enabled and if '-r' option is not used, end of sentences are
used. In this case, this REGEX is imported from GNU Emacs:
[.?!][]\"')}]*\\($\\|\t\\| \\)[ \t\n]*
Whenever GNU extensions are disabled or if '-r' option is used, end
of lines are used; in this case, the default REGEXP is just:
\n
Using an empty REGEXP is equivalent to completely disabling end of
line or end of sentence recognition. In this case, the whole file
is considered to be a single big line or sentence. The user might
want to disallow all truncation flag generation as well, through
option '-F ""'. *Note Syntax of Regular Expressions:
(emacs)Regexps.
When the keywords happen to be near the beginning of the input line
or sentence, this often creates an unused area at the beginning of
the output context line; when the keywords happen to be near the
end of the input line or sentence, this often creates an unused
area at the end of the output context line. The program tries to
fill those unused areas by wrapping around context in them; the
tail of the input line or sentence is used to fill the unused area
on the left of the output line; the head of the input line or
sentence is used to fill the unused area on the right of the output
line.
As a matter of convenience to the user, many usual backslashed
escape sequences from the C language are recognized and converted
to the corresponding characters by 'ptx' itself.
'-W REGEXP'
'--word-regexp=REGEXP'
This option selects which regular expression will describe each
keyword. By default, if GNU extensions are enabled, a word is a
sequence of letters; the REGEXP used is '\w+'. When GNU extensions
are disabled, a word is by default anything which ends with a
space, a tab or a newline; the REGEXP used is '[^ \t\n]+'.
An empty REGEXP is equivalent to not using this option. *Note
Syntax of Regular Expressions: (emacs)Regexps.
As a matter of convenience to the user, many usual backslashed
escape sequences, as found in the C language, are recognized and
converted to the corresponding characters by 'ptx' itself.
Output formatting
-----------------
Output format is mainly controlled by the '-O' and '-T' options
described in the table below. When neither '-O' nor '-T' are selected,
and if GNU extensions are enabled, the program chooses an output format
suitable for a dumb terminal. Each keyword occurrence is output to the
center of one line, surrounded by its left and right contexts. Each
field is properly justified, so the concordance output can be readily
observed. As a special feature, if automatic references are selected by
option '-A' and are output before the left context, that is, if option
'-R' is _not_ selected, then a colon is added after the reference; this
nicely interfaces with GNU Emacs 'next-error' processing. In this
default output format, each white space character, like newline and tab,
is merely changed to exactly one space, with no special attempt to
compress consecutive spaces. This might change in the future. Except
for those white space characters, every other character of the
underlying set of 256 characters is transmitted verbatim.
Output format is further controlled by the following options.
'-g NUMBER'
'--gap-size=NUMBER'
Select the size of the minimum white space gap between the fields
on the output line.
'-w NUMBER'
'--width=NUMBER'
Select the maximum output width of each final line. If references
are used, they are included or excluded from the maximum output
width depending on the value of option '-R'. If this option is not
selected, that is, when references are output before the left
context, the maximum output width takes into account the maximum
length of all references. If this option is selected, that is,
when references are output after the right context, the maximum
output width does not take into account the space taken by
references, nor the gap that precedes them.
'-A'
'--auto-reference'
Select automatic references. Each input line will have an
automatic reference made up of the file name and the line ordinal,
with a single colon between them. However, the file name will be
empty when standard input is being read. If both '-A' and '-r' are
selected, then the input reference is still read and skipped, but
the automatic reference is used at output time, overriding the
input reference.
'-R'
'--right-side-refs'
In the default output format, when option '-R' is not used, any
references produced by the effect of options '-r' or '-A' are
placed to the far right of output lines, after the right context.
With default output format, when the '-R' option is specified,
references are rather placed at the beginning of each output line,
before the left context. For any other output format, option '-R'
is ignored, with one exception: with '-R' the width of references
is _not_ taken into account in total output width given by '-w'.
This option is automatically selected whenever GNU extensions are
disabled.
'-F STRING'
'--flac-truncation=STRING'
This option will request that any truncation in the output be
reported using the string STRING. Most output fields theoretically
extend towards the beginning or the end of the current line, or
current sentence, as selected with option '-S'. But there is a
maximum allowed output line width, changeable through option '-w',
which is further divided into space for various output fields.
When a field has to be truncated because it cannot extend beyond
the beginning or the end of the current line to fit in, then a
truncation occurs. By default, the string used is a single slash,
as in '-F /'.
STRING may have more than one character, as in '-F ...'. Also, in
the particular case when STRING is empty ('-F ""'), truncation
flagging is disabled, and no truncation marks are appended in this
case.
As a matter of convenience to the user, many usual backslashed
escape sequences, as found in the C language, are recognized and
converted to the corresponding characters by 'ptx' itself.
'-M STRING'
'--macro-name=STRING'
Select another STRING to be used instead of 'xx', while generating
output suitable for 'nroff', 'troff' or TeX.
'-O'
'--format=roff'
Choose an output format suitable for 'nroff' or 'troff' processing.
Each output line will look like:
.xx "TAIL" "BEFORE" "KEYWORD_AND_AFTER" "HEAD" "REF"
so it will be possible to write a '.xx' roff macro to take care of
the output typesetting. This is the default output format when GNU
extensions are disabled. Option '-M' can be used to change 'xx' to
another macro name.
In this output format, each non-graphical character, like newline
and tab, is merely changed to exactly one space, with no special
attempt to compress consecutive spaces. Each quote character '"'
is doubled so it will be correctly processed by 'nroff' or 'troff'.
'-T'
'--format=tex'
Choose an output format suitable for TeX processing. Each output
line will look like:
\xx {TAIL}{BEFORE}{KEYWORD}{AFTER}{HEAD}{REF}
so it will be possible to write a '\xx' definition to take care of
the output typesetting. Note that when references are not being
produced, that is, neither option '-A' nor option '-r' is selected,
the last parameter of each '\xx' call is inhibited. Option '-M'
can be used to change 'xx' to another macro name.
In this output format, some special characters, like '$', '%', '&',
'#' and '_' are automatically protected with a backslash. Curly
brackets '{', '}' are protected with a backslash and a pair of
dollar signs (to force mathematical mode). The backslash itself
produces the sequence '\backslash{}'. Circumflex and tilde
diacritical marks produce the sequence '^\{ }' and '~\{ }'
respectively. Other diacriticized characters of the underlying
character set produce an appropriate TeX sequence as far as
possible. The other non-graphical characters, like newline and
tab, and all other characters which are not part of ASCII, are
merely changed to exactly one space, with no special attempt to
compress consecutive spaces. Let me know how to improve this
special character processing for TeX.
The GNU extensions to 'ptx'
---------------------------
This version of 'ptx' contains a few features which do not exist in
System V 'ptx'. These extra features are suppressed by using the '-G'
command line option, unless overridden by other command line options.
Some GNU extensions cannot be recovered by overriding, so the simple
rule is to avoid '-G' if you care about GNU extensions. Here are the
differences between this program and System V 'ptx'.
• This program can read many input files at once, it always writes
the resulting concordance on standard output. On the other hand,
System V 'ptx' reads only one file and sends the result to standard
output or, if a second FILE parameter is given on the command, to
that FILE.
Having output parameters not introduced by options is a dangerous
practice which GNU avoids as far as possible. So, for using 'ptx'
portably between GNU and System V, you should always use it with a
single input file, and always expect the result on standard output.
You might also want to automatically configure in a '-G' option to
'ptx' calls in products using 'ptx', if the configurator finds that
the installed 'ptx' accepts '-G'.
• The only options available in System V 'ptx' are options '-b',
'-f', '-g', '-i', '-o', '-r', '-t' and '-w'. All other options are
GNU extensions and are not repeated in this enumeration. Moreover,
some options have a slightly different meaning when GNU extensions
are enabled, as explained below.
• By default, concordance output is not formatted for 'troff' or
'nroff'. It is rather formatted for a dumb terminal. 'troff' or
'nroff' output may still be selected through option '-O'.
• Unless '-R' option is used, the maximum reference width is
subtracted from the total output line width. With GNU extensions
disabled, width of references is not taken into account in the
output line width computations.
• All 256 bytes, even ASCII NUL bytes, are always read and processed
from input file with no adverse effect, even if GNU extensions are
disabled. However, System V 'ptx' does not accept 8-bit
characters, a few control characters are rejected, and the tilde
'~' is also rejected.
• Input line length is only limited by available memory, even if GNU
extensions are disabled. However, System V 'ptx' processes only
the first 200 characters in each line.
• The break (non-word) characters default to be every character
except all letters of the underlying character set, diacriticized
or not. When GNU extensions are disabled, the break characters
default to space, tab and newline only.
• The program makes better use of output line width. If GNU
extensions are disabled, the program rather tries to imitate System
V 'ptx', but still, there are some slight disposition glitches this
program does not completely reproduce.
• The user can specify both an Ignore file and an Only file. This is
not allowed with System V 'ptx'.
(builtin command)
pushd: pushd [-n] [+N | -N | dir]
Add directories to stack.
Adds a directory to the top of the directory stack, or rotates
the stack, making the new top of the stack the current working
directory. With no arguments, exchanges the top two directories.
Options:
-n Suppresses the normal change of directory when adding
directories to the stack, so only the stack is manipulated.
Arguments:
+N Rotates the stack so that the Nth directory (counting
from the left of the list shown by 'dirs', starting with
zero) is at the top.
-N Rotates the stack so that the Nth directory (counting
from the right of the list shown by 'dirs', starting with
zero) is at the top.
dir Adds DIR to the directory stack at the top, making it the
new current working directory.
The 'dirs' builtin displays the directory stack.
Exit Status:
Returns success unless an invalid argument is supplied or the directory
change fails.
(coreutils)
'pwd': Print working directory
'pwd' prints the name of the current directory. Synopsis:
pwd [OPTION]...
The program accepts the following options. Also see *note Common
options::.
'-L'
'--logical'
If the contents of the environment variable 'PWD' provide an
absolute name of the current directory with no '.' or '..'
components, but possibly with symbolic links, then output those
contents. Otherwise, fall back to default '-P' handling.
'-P'
'--physical'
Print a fully resolved name for the current directory. That is,
all components of the printed name will be actual directory
names—none will be symbolic links.
If '-L' and '-P' are both given, the last one takes precedence. If
neither option is given, then this implementation uses '-P' as the
default unless the 'POSIXLY_CORRECT' environment variable is set.
Due to shell aliases and built-in 'pwd' functions, using an unadorned
'pwd' interactively or in a script may get you different functionality
than that described here. Invoke it via 'env' (i.e., 'env pwd ...') to
avoid interference from the shell.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'pwd': Print working directory
'pwd' prints the name of the current directory. Synopsis:
pwd [OPTION]...
The program accepts the following options. Also see *note Common
options::.
'-L'
'--logical'
If the contents of the environment variable 'PWD' provide an
absolute name of the current directory with no '.' or '..'
components, but possibly with symbolic links, then output those
contents. Otherwise, fall back to default '-P' handling.
'-P'
'--physical'
Print a fully resolved name for the current directory. That is,
all components of the printed name will be actual directory
names—none will be symbolic links.
If '-L' and '-P' are both given, the last one takes precedence. If
neither option is given, then this implementation uses '-P' as the
default unless the 'POSIXLY_CORRECT' environment variable is set.
Due to shell aliases and built-in 'pwd' functions, using an unadorned
'pwd' interactively or in a script may get you different functionality
than that described here. Invoke it via 'env' (i.e., 'env pwd ...') to
avoid interference from the shell.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(builtin command)
read: read [-ers] [-a array] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name ...]
Read a line from the standard input and split it into fields.
Reads a single line from the standard input, or from file descriptor FD
if the -u option is supplied. The line is split into fields as with word
splitting, and the first word is assigned to the first NAME, the second
word to the second NAME, and so on, with any leftover words assigned to
the last NAME. Only the characters found in $IFS are recognized as word
delimiters.
If no NAMEs are supplied, the line read is stored in the REPLY variable.
Options:
-a array assign the words read to sequential indices of the array
variable ARRAY, starting at zero
-d delim continue until the first character of DELIM is read, rather
than newline
-e use Readline to obtain the line in an interactive shell
-i text Use TEXT as the initial text for Readline
-n nchars return after reading NCHARS characters rather than waiting
for a newline, but honor a delimiter if fewer than NCHARS
characters are read before the delimiter
-N nchars return only after reading exactly NCHARS characters, unless
EOF is encountered or read times out, ignoring any delimiter
-p prompt output the string PROMPT without a trailing newline before
attempting to read
-r do not allow backslashes to escape any characters
-s do not echo input coming from a terminal
-t timeout time out and return failure if a complete line of input is
not read within TIMEOUT seconds. The value of the TMOUT
variable is the default timeout. TIMEOUT may be a
fractional number. If TIMEOUT is 0, read returns immediately,
without trying to read any data, returning success only if
input is available on the specified file descriptor. The
exit status is greater than 128 if the timeout is exceeded
-u fd read from file descriptor FD instead of the standard input
Exit Status:
The return code is zero, unless end-of-file is encountered, read times out
(in which case it's greater than 128), a variable assignment error occurs,
or an invalid file descriptor is supplied as the argument to -u.
(builtin command)
readarray: readarray [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
Read lines from a file into an array variable.
A synonym for 'mapfile'.
(coreutils)
'readlink': Print value of a symlink or canonical file name
'readlink' may work in one of two supported modes:
'Readlink mode'
'readlink' outputs the value of the given symbolic links. If
'readlink' is invoked with an argument other than the name of a
symbolic link, it produces no output and exits with a nonzero exit
code.
'Canonicalize mode'
'readlink' outputs the absolute name of the given files which
contain no '.', '..' components nor any repeated separators ('/')
or symbolic links.
readlink [OPTION]... FILE...
By default, 'readlink' operates in readlink mode.
The program accepts the following options. Also see *note Common
options::.
'-f'
'--canonicalize'
Activate canonicalize mode. If any component of the file name
except the last one is missing or unavailable, 'readlink' produces
no output and exits with a nonzero exit code. A trailing slash is
ignored.
'-e'
'--canonicalize-existing'
Activate canonicalize mode. If any component is missing or
unavailable, 'readlink' produces no output and exits with a nonzero
exit code. A trailing slash requires that the name resolve to a
directory.
'-m'
'--canonicalize-missing'
Activate canonicalize mode. If any component is missing or
unavailable, 'readlink' treats it as a directory.
'-n'
'--no-newline'
Do not print the output delimiter, when a single FILE is specified.
Print a warning if specified along with multiple FILEs.
'-s'
'-q'
'--silent'
'--quiet'
Suppress most error messages.
'-v'
'--verbose'
Report error messages.
'-z'
'--zero'
Output a zero byte (ASCII NUL) at the end of each line, rather than
a newline. This option enables other programs to parse the output
even when that output would contain data with embedded newlines.
The 'readlink' utility first appeared in OpenBSD 2.1.
The 'realpath' command without options, operates like 'readlink' in
canonicalize mode.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(builtin command)
readonly: readonly [-aAf] [name[=value] ...] or readonly -p
Mark shell variables as unchangeable.
Mark each NAME as read-only; the values of these NAMEs may not be
changed by subsequent assignment. If VALUE is supplied, assign VALUE
before marking as read-only.
Options:
-a refer to indexed array variables
-A refer to associative array variables
-f refer to shell functions
-p display a list of all readonly variables or functions, depending on
whether or not the -f option is given
An argument of '--' disables further option processing.
Exit Status:
Returns success unless an invalid option is given or NAME is invalid.
(coreutils)
'realpath': Print the resolved file name.
'realpath' expands all symbolic links and resolves references to '/./',
'/../' and extra '/' characters. By default, all but the last component
of the specified files must exist. Synopsis:
realpath [OPTION]... FILE...
The program accepts the following options. Also see *note Common
options::.
'-e'
'--canonicalize-existing'
Ensure that all components of the specified file names exist. If
any component is missing or unavailable, 'realpath' will output a
diagnostic unless the '-q' option is specified, and exit with a
nonzero exit code. A trailing slash requires that the name resolve
to a directory.
'-m'
'--canonicalize-missing'
If any component of a specified file name is missing or
unavailable, treat it as a directory.
'-L'
'--logical'
Symbolic links are resolved in the specified file names, but they
are resolved after any subsequent '..' components are processed.
'-P'
'--physical'
Symbolic links are resolved in the specified file names, and they
are resolved before any subsequent '..' components are processed.
This is the default mode of operation.
'-q'
'--quiet'
Suppress diagnostic messages for specified file names.
'--relative-to=FILE'
Print the resolved file names relative to the specified file. Note
this option honors the '-m' and '-e' options pertaining to file
existence.
'--relative-base=BASE'
This option is valid when used with '--relative-to', and will
restrict the output of '--relative-to' so that relative names are
output, only when FILEs are descendants of BASE. Otherwise output
the absolute file name. If '--relative-to' was not specified, then
the descendants of BASE are printed relative to BASE. If
'--relative-to' is specified, then that directory must be a
descendant of BASE for this option to have an effect. Note: this
option honors the '-m' and '-e' options pertaining to file
existence. For example:
realpath --relative-to=/usr /tmp /usr/bin
⇒ ../tmp
⇒ bin
realpath --relative-base=/usr /tmp /usr/bin
⇒ /tmp
⇒ bin
'-s'
'--strip'
'--no-symlinks'
Do not resolve symbolic links. Only resolve references to '/./',
'/../' and remove extra '/' characters. When combined with the
'-m' option, realpath operates only on the file name, and does not
touch any actual file.
'-z'
'--zero'
Output a zero byte (ASCII NUL) at the end of each line, rather than
a newline. This option enables other programs to parse the output
even when that output would contain data with embedded newlines.
Exit status:
0 if all file names were printed without issue.
1 otherwise.
(builtin command)
return: return [n]
Return from a shell function.
Causes a function or sourced script to exit with the return value
specified by N. If N is omitted, the return status is that of the
last command executed within the function or script.
Exit Status:
Returns N, or failure if the shell is not executing a function or script.
(coreutils)
'rm': Remove files or directories
'rm' removes each given FILE. By default, it does not remove
directories. Synopsis:
rm [OPTION]... [FILE]...
If the '-I' or '--interactive=once' option is given, and there are
more than three files or the '-r', '-R', or '--recursive' are given,
then 'rm' prompts the user for whether to proceed with the entire
operation. If the response is not affirmative, the entire command is
aborted.
Otherwise, if a file is unwritable, standard input is a terminal, and
the '-f' or '--force' option is not given, or the '-i' or
'--interactive=always' option _is_ given, 'rm' prompts the user for
whether to remove the file. If the response is not affirmative, the
file is skipped.
Any attempt to remove a file whose last file name component is '.' or
'..' is rejected without any prompting, as mandated by POSIX.
_Warning_: If you use 'rm' to remove a file, it is usually possible
to recover the contents of that file. If you want more assurance that
the contents are truly unrecoverable, consider using 'shred'.
The program accepts the following options. Also see *note Common
options::.
'-d'
'--dir'
Remove the listed directories if they are empty.
'-f'
'--force'
Ignore nonexistent files and missing operands, and never prompt the
user. Ignore any previous '--interactive' ('-i') option.
'-i'
Prompt whether to remove each file. If the response is not
affirmative, the file is skipped. Ignore any previous '--force'
('-f') option. Equivalent to '--interactive=always'.
'-I'
Prompt once whether to proceed with the command, if more than three
files are named or if a recursive removal is requested. Ignore any
previous '--force' ('-f') option. Equivalent to
'--interactive=once'.
'--interactive [=WHEN]'
Specify when to issue an interactive prompt. WHEN may be omitted,
or one of:
• never - Do not prompt at all.
• once - Prompt once if more than three files are named or if a
recursive removal is requested. Equivalent to '-I'.
• always - Prompt for every file being removed. Equivalent to
'-i'.
'--interactive' with no WHEN is equivalent to
'--interactive=always'.
'--one-file-system'
When removing a hierarchy recursively, skip any directory that is
on a file system different from that of the corresponding command
line argument.
This option is useful when removing a build "chroot" hierarchy,
which normally contains no valuable data. However, it is not
uncommon to bind-mount '/home' into such a hierarchy, to make it
easier to use one's start-up file. The catch is that it's easy to
forget to unmount '/home'. Then, when you use 'rm -rf' to remove
your normally throw-away chroot, that command will remove
everything under '/home', too. Use the '--one-file-system' option,
and it will warn about and skip directories on other file systems.
Of course, this will not save your '/home' if it and your chroot
happen to be on the same file system.
'--preserve-root'
Fail upon any attempt to remove the root directory, '/', when used
with the '--recursive' option. This is the default behavior.
*Note Treating / specially::.
'--no-preserve-root'
Do not treat '/' specially when removing recursively. This option
is not recommended unless you really want to remove all the files
on your computer. *Note Treating / specially::.
'-r'
'-R'
'--recursive'
Remove the listed directories and their contents recursively.
'-v'
'--verbose'
Print the name of each file before removing it.
One common question is how to remove files whose names begin with a
'-'. GNU 'rm', like every program that uses the 'getopt' function to
parse its arguments, lets you use the '--' option to indicate that all
following arguments are non-options. To remove a file called '-f' in
the current directory, you could type either:
rm -- -f
or:
rm ./-f
The Unix 'rm' program's use of a single '-' for this purpose predates
the development of the getopt standard syntax.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'rmdir': Remove empty directories
'rmdir' removes empty directories. Synopsis:
rmdir [OPTION]... DIRECTORY...
If any DIRECTORY argument does not refer to an existing empty
directory, it is an error.
The program accepts the following options. Also see *note Common
options::.
'--ignore-fail-on-non-empty'
Ignore each failure to remove a directory that is solely because
the directory is non-empty.
'-p'
'--parents'
Remove DIRECTORY, then try to remove each component of DIRECTORY.
So, for example, 'rmdir -p a/b/c' is similar to 'rmdir a/b/c a/b
a'. As such, it fails if any of those directories turns out not to
be empty. Use the '--ignore-fail-on-non-empty' option to make it
so such a failure does not evoke a diagnostic and does not cause
'rmdir' to exit unsuccessfully.
'-v'
'--verbose'
Give a diagnostic for each successful removal. DIRECTORY is
removed.
*Note rm invocation::, for how to remove non-empty directories
(recursively).
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'runcon': Run a command in specified SELinux context
'runcon' runs file in specified SELinux security context.
Synopses:
runcon CONTEXT COMMAND [ARGS]
runcon [ -c ] [-u USER] [-r ROLE] [-t TYPE] [-l RANGE] COMMAND [ARGS]
Run COMMAND with completely-specified CONTEXT, or with current or
transitioned security context modified by one or more of LEVEL, ROLE,
TYPE and USER.
If none of '-c', '-t', '-u', '-r', or '-l' is specified, the first
argument is used as the complete context. Any additional arguments
after COMMAND are interpreted as arguments to the command.
With neither CONTEXT nor COMMAND, print the current security context.
The program accepts the following options. Also see *note Common
options::.
'-c'
'--compute'
Compute process transition context before modifying.
'-u USER'
'--user=USER'
Set user USER in the target security context.
'-r ROLE'
'--role=ROLE'
Set role ROLE in the target security context.
'-t TYPE'
'--type=TYPE'
Set type TYPE in the target security context.
'-l RANGE'
'--range=RANGE'
Set range RANGE in the target security context.
Exit status:
126 if COMMAND is found but cannot be invoked
127 if 'runcon' itself fails or if COMMAND cannot be found
the exit status of COMMAND otherwise
(reserved word)
select: select NAME [in WORDS ... ;] do COMMANDS; done
Select words from a list and execute commands.
The WORDS are expanded, generating a list of words. The
set of expanded words is printed on the standard error, each
preceded by a number. If 'in WORDS' is not present, 'in "$@"'
is assumed. The PS3 prompt is then displayed and a line read
from the standard input. If the line consists of the number
corresponding to one of the displayed words, then NAME is set
to that word. If the line is empty, WORDS and the prompt are
redisplayed. If EOF is read, the command completes. Any other
value read causes NAME to be set to null. The line read is saved
in the variable REPLY. COMMANDS are executed after each selection
until a break command is executed.
Exit Status:
Returns the status of the last command executed.
(coreutils)
'seq': Print numeric sequences
'seq' prints a sequence of numbers to standard output. Synopses:
seq [OPTION]... LAST
seq [OPTION]... FIRST LAST
seq [OPTION]... FIRST INCREMENT LAST
'seq' prints the numbers from FIRST to LAST by INCREMENT. By
default, each number is printed on a separate line. When INCREMENT is
not specified, it defaults to '1', even when FIRST is larger than LAST.
FIRST also defaults to '1'. So 'seq 1' prints '1', but 'seq 0' and 'seq
10 5' produce no output. The sequence of numbers ends when the sum of
the current number and INCREMENT would become greater than LAST, so 'seq
1 10 10' only produces '1'. Floating-point numbers may be specified.
*Note Floating point::.
The program accepts the following options. Also see *note Common
options::. Options must precede operands.
'-f FORMAT'
'--format=FORMAT'
Print all numbers using FORMAT. FORMAT must contain exactly one of
the 'printf'-style floating point conversion specifications '%a',
'%e', '%f', '%g', '%A', '%E', '%F', '%G'. The '%' may be followed
by zero or more flags taken from the set '-+#0 '', then an optional
width containing one or more digits, then an optional precision
consisting of a '.' followed by zero or more digits. FORMAT may
also contain any number of '%%' conversion specifications. All
conversion specifications have the same meaning as with 'printf'.
The default format is derived from FIRST, STEP, and LAST. If these
all use a fixed point decimal representation, the default format is
'%.Pf', where P is the minimum precision that can represent the
output numbers exactly. Otherwise, the default format is '%g'.
'-s STRING'
'--separator=STRING'
Separate numbers with STRING; default is a newline. The output
always terminates with a newline.
'-w'
'--equal-width'
Print all numbers with the same width, by padding with leading
zeros. FIRST, STEP, and LAST should all use a fixed point decimal
representation. (To have other kinds of padding, use '--format').
You can get finer-grained control over output with '-f':
$ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
(-9.00E+05)
( 2.00E+05)
( 1.30E+06)
If you want hexadecimal integer output, you can use 'printf' to
perform the conversion:
$ printf '%x\n' $(seq 1048575 1024 1050623)
fffff
1003ff
1007ff
For very long lists of numbers, use xargs to avoid system limitations
on the length of an argument list:
$ seq 1000000 | xargs printf '%x\n' | tail -n 3
f423e
f423f
f4240
To generate octal output, use the printf '%o' format instead of '%x'.
On most systems, seq can produce whole-number output for values up to
at least 2^{53}. Larger integers are approximated. The details differ
depending on your floating-point implementation. *Note Floating
point::. A common case is that 'seq' works with integers through
2^{64}, and larger integers may not be numerically correct:
$ seq 50000000000000000000 2 50000000000000000004
50000000000000000000
50000000000000000000
50000000000000000004
However, note that when limited to non-negative whole numbers, an
increment of 1 and no format-specifying option, seq can print
arbitrarily large numbers.
Be careful when using 'seq' with outlandish values: otherwise you may
see surprising results, as 'seq' uses floating point internally. For
example, on the x86 platform, where the internal representation uses a
64-bit fraction, the command:
seq 1 0.0000000000000000001 1.0000000000000000009
outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(builtin command)
set: set [-abefhkmnptuvxBCHP] [-o option-name] [--] [arg ...]
Set or unset values of shell options and positional parameters.
Change the value of shell attributes and positional parameters, or
display the names and values of shell variables.
Options:
-a Mark variables which are modified or created for export.
-b Notify of job termination immediately.
-e Exit immediately if a command exits with a non-zero status.
-f Disable file name generation (globbing).
-h Remember the location of commands as they are looked up.
-k All assignment arguments are placed in the environment for a
command, not just those that precede the command name.
-m Job control is enabled.
-n Read commands but do not execute them.
-o option-name
Set the variable corresponding to option-name:
allexport same as -a
braceexpand same as -B
emacs use an emacs-style line editing interface
errexit same as -e
errtrace same as -E
functrace same as -T
hashall same as -h
histexpand same as -H
history enable command history
ignoreeof the shell will not exit upon reading EOF
interactive-comments
allow comments to appear in interactive commands
keyword same as -k
monitor same as -m
noclobber same as -C
noexec same as -n
noglob same as -f
nolog currently accepted but ignored
notify same as -b
nounset same as -u
onecmd same as -t
physical same as -P
pipefail the return value of a pipeline is the status of
the last command to exit with a non-zero status,
or zero if no command exited with a non-zero status
posix change the behavior of bash where the default
operation differs from the Posix standard to
match the standard
privileged same as -p
verbose same as -v
vi use a vi-style line editing interface
xtrace same as -x
-p Turned on whenever the real and effective user ids do not match.
Disables processing of the $ENV file and importing of shell
functions. Turning this option off causes the effective uid and
gid to be set to the real uid and gid.
-t Exit after reading and executing one command.
-u Treat unset variables as an error when substituting.
-v Print shell input lines as they are read.
-x Print commands and their arguments as they are executed.
-B the shell will perform brace expansion
-C If set, disallow existing regular files to be overwritten
by redirection of output.
-E If set, the ERR trap is inherited by shell functions.
-H Enable ! style history substitution. This flag is on
by default when the shell is interactive.
-P If set, do not resolve symbolic links when executing commands
such as cd which change the current directory.
-T If set, the DEBUG trap is inherited by shell functions.
-- Assign any remaining arguments to the positional parameters.
If there are no remaining arguments, the positional parameters
are unset.
- Assign any remaining arguments to the positional parameters.
The -x and -v options are turned off.
Using + rather than - causes these flags to be turned off. The
flags can also be used upon invocation of the shell. The current
set of flags may be found in $-. The remaining n ARGs are positional
parameters and are assigned, in order, to $1, $2, .. $n. If no
ARGs are given, all shell variables are printed.
Exit Status:
Returns success unless an invalid option is given.
(coreutils)
'sha1sum': Print or check SHA-1 digests 'sha1sum' computes a 160-bit checksum for each specified FILE. The usage and options of this command are precisely the same as for 'md5sum'. *Note md5sum invocation::. Note: The SHA-1 digest is more secure than MD5, and no collisions of it are known (different files having the same fingerprint). However, it is known that they can be produced with considerable, but not unreasonable, resources. For this reason, it is generally considered that SHA-1 should be gradually phased out in favor of the more secure SHA-2 hash algorithms. *Note sha2 utilities::.
(coreutils)
sha2 utilities: Print or check SHA-2 digests The commands 'sha224sum', 'sha256sum', 'sha384sum' and 'sha512sum' compute checksums of various lengths (respectively 224, 256, 384 and 512 bits), collectively known as the SHA-2 hashes. The usage and options of these commands are precisely the same as for 'md5sum'. *Note md5sum invocation::. Note: The SHA384 and SHA512 digests are considerably slower to compute, especially on 32-bit computers, than SHA224 or SHA256.
(builtin command)
shift: shift [n]
Shift positional parameters.
Rename the positional parameters $N+1,$N+2 ... to $1,$2 ... If N is
not given, it is assumed to be 1.
Exit Status:
Returns success unless N is negative or greater than $#.
(builtin command)
shopt: shopt [-pqsu] [-o] [optname ...]
Set and unset shell options.
Change the setting of each shell option OPTNAME. Without any option
arguments, list all shell options with an indication of whether or not each
is set.
Options:
-o restrict OPTNAMEs to those defined for use with 'set -o'
-p print each shell option with an indication of its status
-q suppress output
-s enable (set) each OPTNAME
-u disable (unset) each OPTNAME
Exit Status:
Returns success if OPTNAME is enabled; fails if an invalid option is
given or OPTNAME is disabled.
(coreutils)
'shred': Remove files more securely
'shred' overwrites devices or files, to help prevent even very expensive
hardware from recovering the data.
Ordinarily when you remove a file (*note rm invocation::), the data
is not actually destroyed. Only the index listing where the file is
stored is destroyed, and the storage is made available for reuse. There
are undelete utilities that will attempt to reconstruct the index and
can bring the file back if the parts were not reused.
On a busy system with a nearly-full drive, space can get reused in a
few seconds. But there is no way to know for sure. If you have
sensitive data, you may want to be sure that recovery is not possible by
actually overwriting the file with non-sensitive data.
However, even after doing that, it is possible to take the disk back
to a laboratory and use a lot of sensitive (and expensive) equipment to
look for the faint "echoes" of the original data underneath the
overwritten data. If the data has only been overwritten once, it's not
even that hard.
The best way to remove something irretrievably is to destroy the
media it's on with acid, melt it down, or the like. For cheap removable
media like floppy disks, this is the preferred method. However, hard
drives are expensive and hard to melt, so the 'shred' utility tries to
achieve a similar effect non-destructively.
This uses many overwrite passes, with the data patterns chosen to
maximize the damage they do to the old data. While this will work on
floppies, the patterns are designed for best effect on hard drives. For
more details, see the source code and Peter Gutmann's paper 'Secure
Deletion of Data from Magnetic and Solid-State Memory'
(http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html), from the
proceedings of the Sixth USENIX Security Symposium (San Jose,
California, July 22–25, 1996).
*Please note* that 'shred' relies on a very important assumption:
that the file system overwrites data in place. This is the traditional
way to do things, but many modern file system designs do not satisfy
this assumption. Exceptions include:
• Log-structured or journaled file systems, such as those supplied
with AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in
'data=journal' mode), BFS, NTFS, etc., when they are configured to
journal _data_.
• File systems that write redundant data and carry on even if some
writes fail, such as RAID-based file systems.
• File systems that make snapshots, such as Network Appliance's NFS
server.
• File systems that cache in temporary locations, such as NFS version
3 clients.
• Compressed file systems.
In the particular case of ext3 file systems, the above disclaimer
applies (and 'shred' is thus of limited effectiveness) only in
'data=journal' mode, which journals file data in addition to just
metadata. In both the 'data=ordered' (default) and 'data=writeback'
modes, 'shred' works as usual. Ext3 journaling modes can be changed by
adding the 'data=something' option to the mount options for a particular
file system in the '/etc/fstab' file, as documented in the mount man
page (man mount).
If you are not sure how your file system operates, then you should
assume that it does not overwrite data in place, which means that shred
cannot reliably operate on regular files in your file system.
Generally speaking, it is more reliable to shred a device than a
file, since this bypasses the problem of file system design mentioned
above. However, even shredding devices is not always completely
reliable. For example, most disks map out bad sectors invisibly to the
application; if the bad sectors contain sensitive data, 'shred' won't be
able to destroy it.
'shred' makes no attempt to detect or report this problem, just as it
makes no attempt to do anything about backups. However, since it is
more reliable to shred devices than files, 'shred' by default does not
truncate or remove the output file. This default is more suitable for
devices, which typically cannot be truncated and should not be removed.
Finally, consider the risk of backups and mirrors. File system
backups and remote mirrors may contain copies of the file that cannot be
removed, and that will allow a shredded file to be recovered later. So
if you keep any data you may later want to destroy using 'shred', be
sure that it is not backed up or mirrored.
shred [OPTION]... FILE[...]
The program accepts the following options. Also see *note Common
options::.
'-f'
'--force'
Override file permissions if necessary to allow overwriting.
'-NUMBER'
'-n NUMBER'
'--iterations=NUMBER'
By default, 'shred' uses 3 passes of overwrite. You can reduce
this to save time, or increase it if you think it's appropriate.
After 25 passes all of the internal overwrite patterns will have
been used at least once.
'--random-source=FILE'
Use FILE as a source of random data used to overwrite and to choose
pass ordering. *Note Random sources::.
'-s BYTES'
'--size=BYTES'
Shred the first BYTES bytes of the file. The default is to shred
the whole file. BYTES can be followed by a size specification like
'K', 'M', or 'G' to specify a multiple. *Note Block size::.
'-u'
'--remove[=HOW]'
After shredding a file, truncate it (if possible) and then remove
it. If a file has multiple links, only the named links will be
removed. Often the file name is less sensitive than the file data,
in which case the optional HOW parameter gives control of how to
more efficiently remove each directory entry. The 'unlink'
parameter will just use a standard unlink call, 'wipe' will also
first obfuscate bytes in the name, and 'wipesync' will also sync
each obfuscated byte in the name to disk. Note 'wipesync' is the
default method, but can be expensive, requiring a sync for every
character in every file. This can become significant with many
files, or is redundant if your file system provides synchronous
metadata updates.
'-v'
'--verbose'
Display to standard error all status updates as sterilization
proceeds.
'-x'
'--exact'
By default, 'shred' rounds the size of a regular file up to the
next multiple of the file system block size to fully erase the
slack space in the last block of the file. This space may contain
portions of the current system memory on some systems for example.
Use '--exact' to suppress that behavior. Thus, by default if you
shred a 10-byte regular file on a system with 512-byte blocks, the
resulting file will be 512 bytes long. With this option, shred
does not increase the apparent size of the file.
'-z'
'--zero'
Normally, the last pass that 'shred' writes is made up of random
data. If this would be conspicuous on your hard drive (for
example, because it looks like encrypted data), or you just think
it's tidier, the '--zero' option adds an additional overwrite pass
with all zero bits. This is in addition to the number of passes
specified by the '--iterations' option.
You might use the following command to erase all trace of the file
system you'd created on the floppy disk in your first drive. That
command takes about 20 minutes to erase a "1.44MB" (actually 1440 KiB)
floppy.
shred --verbose /dev/fd0
Similarly, to erase all data on a selected partition of your hard
disk, you could give a command like this:
shred --verbose /dev/sda5
On modern disks, a single pass should be adequate, and it will take
one third the time of the default three-pass approach.
# 1 pass, write pseudo-random data; 3x faster than the default
shred --verbose -n1 /dev/sda5
To be on the safe side, use at least one pass that overwrites using
pseudo-random data. I.e., don't be tempted to use '-n0 --zero', in case
some disk controller optimizes the process of writing blocks of all
zeros, and thereby does not clear all bytes in a block. Some SSDs may
do just that.
A FILE of '-' denotes standard output. The intended use of this is
to shred a removed temporary file. For example:
i=$(mktemp)
exec 3<>"$i"
rm -- "$i"
echo "Hello, world" >&3
shred - >&3
exec 3>-
However, the command 'shred - >file' does not shred the contents of
FILE, since the shell truncates FILE before invoking 'shred'. Use the
command 'shred file' or (if using a Bourne-compatible shell) the command
'shred - 1<>file' instead.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'shuf': Shuffling text
'shuf' shuffles its input by outputting a random permutation of its
input lines. Each output permutation is equally likely. Synopses:
shuf [OPTION]... [FILE]
shuf -e [OPTION]... [ARG]...
shuf -i LO-HI [OPTION]...
'shuf' has three modes of operation that affect where it obtains its
input lines. By default, it reads lines from standard input. The
following options change the operation mode:
'-e'
'--echo'
Treat each command-line operand as an input line.
'-i LO-HI'
'--input-range=LO-HI'
Act as if input came from a file containing the range of unsigned
decimal integers LO...HI, one per line.
'shuf''s other options can affect its behavior in all operation
modes:
'-n LINES'
'--head-count=COUNT'
Output at most COUNT lines. By default, all input lines are
output.
'-o OUTPUT-FILE'
'--output=OUTPUT-FILE'
Write output to OUTPUT-FILE instead of standard output. 'shuf'
reads all input before opening OUTPUT-FILE, so you can safely
shuffle a file in place by using commands like 'shuf -o F <F' and
'cat F | shuf -o F'.
'--random-source=FILE'
Use FILE as a source of random data used to determine which
permutation to generate. *Note Random sources::.
'-r'
'--repeat'
Repeat output values, that is, select with replacement. With this
option the output is not a permutation of the input; instead, each
output line is randomly chosen from all the inputs. This option is
typically combined with '--head-count'; if '--head-count' is not
given, 'shuf' repeats indefinitely.
'-z'
'--zero-terminated'
Delimit items with a zero byte rather than a newline (ASCII LF).
I.e., treat input as items separated by ASCII NUL and terminate
output items with ASCII NUL. This option can be useful in
conjunction with 'perl -0' or 'find -print0' and 'xargs -0' which
do the same in order to reliably handle arbitrary file names (even
those containing blanks or other special characters).
For example:
shuf <<EOF
A man,
a plan,
a canal:
Panama!
EOF
might produce the output
Panama!
A man,
a canal:
a plan,
Similarly, the command:
shuf -e clubs hearts diamonds spades
might output:
clubs
diamonds
spades
hearts
and the command 'shuf -i 1-4' might output:
4
2
1
3
The above examples all have four input lines, so 'shuf' might produce
any of the twenty-four possible permutations of the input. In general,
if there are N input lines, there are N! (i.e., N factorial, or N * (N
- 1) * ... * 1) possible output permutations.
To output 50 random numbers each in the range 0 through 9, use:
shuf -r -n 50 -i 0-9
To simulate 100 coin flips, use:
shuf -r -n 100 -e Head Tail
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'sleep': Delay for a specified time
'sleep' pauses for an amount of time specified by the sum of the values
of the command line arguments. Synopsis:
sleep NUMBER[smhd]...
Each argument is a number followed by an optional unit; the default
is seconds. The units are:
's'
seconds
'm'
minutes
'h'
hours
'd'
days
Historical implementations of 'sleep' have required that NUMBER be an
integer, and only accepted a single argument without a suffix. However,
GNU 'sleep' accepts arbitrary floating point numbers. *Note Floating
point::.
The only options are '--help' and '--version'. *Note Common
options::.
Due to shell aliases and built-in 'sleep' functions, using an
unadorned 'sleep' interactively or in a script may get you different
functionality than that described here. Invoke it via 'env' (i.e., 'env
sleep ...') to avoid interference from the shell.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'sort': Sort text files
'sort' sorts, merges, or compares all the lines from the given files, or
standard input if none are given or for a FILE of '-'. By default,
'sort' writes the results to standard output. Synopsis:
sort [OPTION]... [FILE]...
'sort' has three modes of operation: sort (the default), merge, and
check for sortedness. The following options change the operation mode:
'-c'
'--check'
'--check=diagnose-first'
Check whether the given file is already sorted: if it is not all
sorted, print a diagnostic containing the first out-of-order line
and exit with a status of 1. Otherwise, exit successfully. At
most one input file can be given.
'-C'
'--check=quiet'
'--check=silent'
Exit successfully if the given file is already sorted, and exit
with status 1 otherwise. At most one input file can be given.
This is like '-c', except it does not print a diagnostic.
'-m'
'--merge'
Merge the given files by sorting them as a group. Each input file
must always be individually sorted. It always works to sort
instead of merge; merging is provided because it is faster, in the
case where it works.
A pair of lines is compared as follows: 'sort' compares each pair of
fields, in the order specified on the command line, according to the
associated ordering options, until a difference is found or no fields
are left. If no key fields are specified, 'sort' uses a default key of
the entire line. Finally, as a last resort when all keys compare equal,
'sort' compares entire lines as if no ordering options other than
'--reverse' ('-r') were specified. The '--stable' ('-s') option
disables this "last-resort comparison" so that lines in which all fields
compare equal are left in their original relative order. The '--unique'
('-u') option also disables the last-resort comparison.
Unless otherwise specified, all comparisons use the character
collating sequence specified by the 'LC_COLLATE' locale.(1)
GNU 'sort' (as specified for all GNU utilities) has no limit on input
line length or restrictions on bytes allowed within lines. In addition,
if the final byte of an input file is not a newline, GNU 'sort' silently
supplies one. A line's trailing newline is not part of the line for
comparison purposes.
Exit status:
0 if no error occurred
1 if invoked with '-c' or '-C' and the input is not sorted
2 if an error occurred
If the environment variable 'TMPDIR' is set, 'sort' uses its value as
the directory for temporary files instead of '/tmp'. The
'--temporary-directory' ('-T') option in turn overrides the environment
variable.
The following options affect the ordering of output lines. They may
be specified globally or as part of a specific key field. If no key
fields are specified, global options apply to comparison of entire
lines; otherwise the global options are inherited by key fields that do
not specify any special options of their own. In pre-POSIX versions of
'sort', global options affect only later key fields, so portable shell
scripts should specify global options first.
'-b'
'--ignore-leading-blanks'
Ignore leading blanks when finding sort keys in each line. By
default a blank is a space or a tab, but the 'LC_CTYPE' locale can
change this. Note blanks may be ignored by your locale's collating
rules, but without this option they will be significant for
character positions specified in keys with the '-k' option.
'-d'
'--dictionary-order'
Sort in "phone directory" order: ignore all characters except
letters, digits and blanks when sorting. By default letters and
digits are those of ASCII and a blank is a space or a tab, but the
'LC_CTYPE' locale can change this.
'-f'
'--ignore-case'
Fold lowercase characters into the equivalent uppercase characters
when comparing so that, for example, 'b' and 'B' sort as equal.
The 'LC_CTYPE' locale determines character types. When used with
'--unique' those lower case equivalent lines are thrown away.
(There is currently no way to throw away the upper case equivalent
instead. (Any '--reverse' given would only affect the final
result, after the throwing away.))
'-g'
'--general-numeric-sort'
'--sort=general-numeric'
Sort numerically, converting a prefix of each line to a long
double-precision floating point number. *Note Floating point::.
Do not report overflow, underflow, or conversion errors. Use the
following collating sequence:
• Lines that do not start with numbers (all considered to be
equal).
• NaNs ("Not a Number" values, in IEEE floating point
arithmetic) in a consistent but machine-dependent order.
• Minus infinity.
• Finite numbers in ascending numeric order (with -0 and +0
equal).
• Plus infinity.
Use this option only if there is no alternative; it is much slower
than '--numeric-sort' ('-n') and it can lose information when
converting to floating point.
'-h'
'--human-numeric-sort'
'--sort=human-numeric'
Sort numerically, first by numeric sign (negative, zero, or
positive); then by SI suffix (either empty, or 'k' or 'K', or one
of 'MGTPEZY', in that order; *note Block size::); and finally by
numeric value. For example, '1023M' sorts before '1G' because 'M'
(mega) precedes 'G' (giga) as an SI suffix. This option sorts
values that are consistently scaled to the nearest suffix,
regardless of whether suffixes denote powers of 1000 or 1024, and
it therefore sorts the output of any single invocation of the 'df',
'du', or 'ls' commands that are invoked with their
'--human-readable' or '--si' options. The syntax for numbers is
the same as for the '--numeric-sort' option; the SI suffix must
immediately follow the number. Note also the 'numfmt' command,
which can be used to reformat numbers to human format _after_ the
sort, thus often allowing sort to operate on more accurate numbers.
'-i'
'--ignore-nonprinting'
Ignore nonprinting characters. The 'LC_CTYPE' locale determines
character types. This option has no effect if the stronger
'--dictionary-order' ('-d') option is also given.
'-M'
'--month-sort'
'--sort=month'
An initial string, consisting of any amount of blanks, followed by
a month name abbreviation, is folded to UPPER case and compared in
the order 'JAN' < 'FEB' < ... < 'DEC'. Invalid names compare low to
valid names. The 'LC_TIME' locale category determines the month
spellings. By default a blank is a space or a tab, but the
'LC_CTYPE' locale can change this.
'-n'
'--numeric-sort'
'--sort=numeric'
Sort numerically. The number begins each line and consists of
optional blanks, an optional '-' sign, and zero or more digits
possibly separated by thousands separators, optionally followed by
a decimal-point character and zero or more digits. An empty number
is treated as '0'. The 'LC_NUMERIC' locale specifies the
decimal-point character and thousands separator. By default a
blank is a space or a tab, but the 'LC_CTYPE' locale can change
this.
Comparison is exact; there is no rounding error.
Neither a leading '+' nor exponential notation is recognized. To
compare such strings numerically, use the '--general-numeric-sort'
('-g') option.
'-V'
'--version-sort'
Sort by version name and number. It behaves like a standard sort,
except that each sequence of decimal digits is treated numerically
as an index/version number. (*Note Details about version sort::.)
'-r'
'--reverse'
Reverse the result of comparison, so that lines with greater key
values appear earlier in the output instead of later.
'-R'
'--random-sort'
'--sort=random'
Sort by hashing the input keys and then sorting the hash values.
Choose the hash function at random, ensuring that it is free of
collisions so that differing keys have differing hash values. This
is like a random permutation of the inputs (*note shuf
invocation::), except that keys with the same value sort together.
If multiple random sort fields are specified, the same random hash
function is used for all fields. To use different random hash
functions for different fields, you can invoke 'sort' more than
once.
The choice of hash function is affected by the '--random-source'
option.
Other options are:
'--compress-program=PROG'
Compress any temporary files with the program PROG.
With no arguments, PROG must compress standard input to standard
output, and when given the '-d' option it must decompress standard
input to standard output.
Terminate with an error if PROG exits with nonzero status.
White space and the backslash character should not appear in PROG;
they are reserved for future use.
'--files0-from=FILE'
Disallow processing files named on the command line, and instead
process those named in file FILE; each name being terminated by a
zero byte (ASCII NUL). This is useful when the list of file names
is so long that it may exceed a command line length limitation. In
such cases, running 'sort' via 'xargs' is undesirable because it
splits the list into pieces and makes 'sort' print sorted output
for each sublist rather than for the entire list. One way to
produce a list of ASCII NUL terminated file names is with GNU
'find', using its '-print0' predicate. If FILE is '-' then the
ASCII NUL terminated file names are read from standard input.
'-k POS1[,POS2]'
'--key=POS1[,POS2]'
Specify a sort field that consists of the part of the line between
POS1 and POS2 (or the end of the line, if POS2 is omitted),
_inclusive_.
Each POS has the form 'F[.C][OPTS]', where F is the number of the
field to use, and C is the number of the first character from the
beginning of the field. Fields and character positions are
numbered starting with 1; a character position of zero in POS2
indicates the field's last character. If '.C' is omitted from
POS1, it defaults to 1 (the beginning of the field); if omitted
from POS2, it defaults to 0 (the end of the field). OPTS are
ordering options, allowing individual keys to be sorted according
to different rules; see below for details. Keys can span multiple
fields.
Example: To sort on the second field, use '--key=2,2' ('-k 2,2').
See below for more notes on keys and more examples. See also the
'--debug' option to help determine the part of the line being used
in the sort.
'--debug'
Highlight the portion of each line used for sorting. Also issue
warnings about questionable usage to stderr.
'--batch-size=NMERGE'
Merge at most NMERGE inputs at once.
When 'sort' has to merge more than NMERGE inputs, it merges them in
groups of NMERGE, saving the result in a temporary file, which is
then used as an input in a subsequent merge.
A large value of NMERGE may improve merge performance and decrease
temporary storage utilization at the expense of increased memory
usage and I/O. Conversely a small value of NMERGE may reduce
memory requirements and I/O at the expense of temporary storage
consumption and merge performance.
The value of NMERGE must be at least 2. The default value is
currently 16, but this is implementation-dependent and may change
in the future.
The value of NMERGE may be bounded by a resource limit for open
file descriptors. The commands 'ulimit -n' or 'getconf OPEN_MAX'
may display limits for your systems; these limits may be modified
further if your program already has some files open, or if the
operating system has other limits on the number of open files. If
the value of NMERGE exceeds the resource limit, 'sort' silently
uses a smaller value.
'-o OUTPUT-FILE'
'--output=OUTPUT-FILE'
Write output to OUTPUT-FILE instead of standard output. Normally,
'sort' reads all input before opening OUTPUT-FILE, so you can
safely sort a file in place by using commands like 'sort -o F F'
and 'cat F | sort -o F'. However, 'sort' with '--merge' ('-m') can
open the output file before reading all input, so a command like
'cat F | sort -m -o F - G' is not safe as 'sort' might start
writing 'F' before 'cat' is done reading it.
On newer systems, '-o' cannot appear after an input file if
'POSIXLY_CORRECT' is set, e.g., 'sort F -o F'. Portable scripts
should specify '-o OUTPUT-FILE' before any input files.
'--random-source=FILE'
Use FILE as a source of random data used to determine which random
hash function to use with the '-R' option. *Note Random sources::.
'-s'
'--stable'
Make 'sort' stable by disabling its last-resort comparison. This
option has no effect if no fields or global ordering options other
than '--reverse' ('-r') are specified.
'-S SIZE'
'--buffer-size=SIZE'
Use a main-memory sort buffer of the given SIZE. By default, SIZE
is in units of 1024 bytes. Appending '%' causes SIZE to be
interpreted as a percentage of physical memory. Appending 'K'
multiplies SIZE by 1024 (the default), 'M' by 1,048,576, 'G' by
1,073,741,824, and so on for 'T', 'P', 'E', 'Z', and 'Y'.
Appending 'b' causes SIZE to be interpreted as a byte count, with
no multiplication.
This option can improve the performance of 'sort' by causing it to
start with a larger or smaller sort buffer than the default.
However, this option affects only the initial buffer size. The
buffer grows beyond SIZE if 'sort' encounters input lines larger
than SIZE.
'-t SEPARATOR'
'--field-separator=SEPARATOR'
Use character SEPARATOR as the field separator when finding the
sort keys in each line. By default, fields are separated by the
empty string between a non-blank character and a blank character.
By default a blank is a space or a tab, but the 'LC_CTYPE' locale
can change this.
That is, given the input line ' foo bar', 'sort' breaks it into
fields ' foo' and ' bar'. The field separator is not considered to
be part of either the field preceding or the field following, so
with 'sort -t " "' the same input line has three fields: an empty
field, 'foo', and 'bar'. However, fields that extend to the end of
the line, as '-k 2', or fields consisting of a range, as '-k 2,3',
retain the field separators present between the endpoints of the
range.
To specify ASCII NUL as the field separator, use the two-character
string '\0', e.g., 'sort -t '\0''.
'-T TEMPDIR'
'--temporary-directory=TEMPDIR'
Use directory TEMPDIR to store temporary files, overriding the
'TMPDIR' environment variable. If this option is given more than
once, temporary files are stored in all the directories given. If
you have a large sort or merge that is I/O-bound, you can often
improve performance by using this option to specify directories on
different disks and controllers.
'--parallel=N'
Set the number of sorts run in parallel to N. By default, N is set
to the number of available processors, but limited to 8, as there
are diminishing performance gains after that. Note also that using
N threads increases the memory usage by a factor of log N. Also
see *note nproc invocation::.
'-u'
'--unique'
Normally, output only the first of a sequence of lines that compare
equal. For the '--check' ('-c' or '-C') option, check that no pair
of consecutive lines compares equal.
This option also disables the default last-resort comparison.
The commands 'sort -u' and 'sort | uniq' are equivalent, but this
equivalence does not extend to arbitrary 'sort' options. For
example, 'sort -n -u' inspects only the value of the initial
numeric string when checking for uniqueness, whereas 'sort -n |
uniq' inspects the entire line. *Note uniq invocation::.
'-z'
'--zero-terminated'
Delimit items with a zero byte rather than a newline (ASCII LF).
I.e., treat input as items separated by ASCII NUL and terminate
output items with ASCII NUL. This option can be useful in
conjunction with 'perl -0' or 'find -print0' and 'xargs -0' which
do the same in order to reliably handle arbitrary file names (even
those containing blanks or other special characters).
Historical (BSD and System V) implementations of 'sort' have differed
in their interpretation of some options, particularly '-b', '-f', and
'-n'. GNU sort follows the POSIX behavior, which is usually (but not
always!) like the System V behavior. According to POSIX, '-n' no
longer implies '-b'. For consistency, '-M' has been changed in the same
way. This may affect the meaning of character positions in field
specifications in obscure cases. The only fix is to add an explicit
'-b'.
A position in a sort field specified with '-k' may have any of the
option letters 'MbdfghinRrV' appended to it, in which case no global
ordering options are inherited by that particular field. The '-b'
option may be independently attached to either or both of the start and
end positions of a field specification, and if it is inherited from the
global options it will be attached to both. If input lines can contain
leading or adjacent blanks and '-t' is not used, then '-k' is typically
combined with '-b' or an option that implicitly ignores leading blanks
('Mghn') as otherwise the varying numbers of leading blanks in fields
can cause confusing results.
If the start position in a sort field specifier falls after the end
of the line or after the end field, the field is empty. If the '-b'
option was specified, the '.C' part of a field specification is counted
from the first nonblank character of the field.
On older systems, 'sort' supports an obsolete origin-zero syntax
'+POS1 [-POS2]' for specifying sort keys. The obsolete sequence 'sort
+A.X -B.Y' is equivalent to 'sort -k A+1.X+1,B' if Y is '0' or absent,
otherwise it is equivalent to 'sort -k A+1.X+1,B+1.Y'.
This obsolete behavior can be enabled or disabled with the
'_POSIX2_VERSION' environment variable (*note Standards conformance::);
it can also be enabled when 'POSIXLY_CORRECT' is not set by using the
obsolete syntax with '-POS2' present.
Scripts intended for use on standard hosts should avoid obsolete
syntax and should use '-k' instead. For example, avoid 'sort +2', since
it might be interpreted as either 'sort ./+2' or 'sort -k 3'. If your
script must also run on hosts that support only the obsolete syntax, it
can use a test like 'if sort -k 1 </dev/null >/dev/null 2>&1; then ...' to
decide which syntax to use.
Here are some examples to illustrate various combinations of options.
• Sort in descending (reverse) numeric order.
sort -n -r
• Run no more than 4 sorts concurrently, using a buffer size of 10M.
sort --parallel=4 -S 10M
• Sort alphabetically, omitting the first and second fields and the
blanks at the start of the third field. This uses a single key
composed of the characters beginning at the start of the first
nonblank character in field three and extending to the end of each
line.
sort -k 3b
• Sort numerically on the second field and resolve ties by sorting
alphabetically on the third and fourth characters of field five.
Use ':' as the field delimiter.
sort -t : -k 2,2n -k 5.3,5.4
Note that if you had written '-k 2n' instead of '-k 2,2n' 'sort'
would have used all characters beginning in the second field and
extending to the end of the line as the primary _numeric_ key. For
the large majority of applications, treating keys spanning more
than one field as numeric will not do what you expect.
Also note that the 'n' modifier was applied to the field-end
specifier for the first key. It would have been equivalent to
specify '-k 2n,2' or '-k 2n,2n'. All modifiers except 'b' apply to
the associated _field_, regardless of whether the modifier
character is attached to the field-start and/or the field-end part
of the key specifier.
• Sort the password file on the fifth field and ignore any leading
blanks. Sort lines with equal values in field five on the numeric
user ID in field three. Fields are separated by ':'.
sort -t : -k 5b,5 -k 3,3n /etc/passwd
sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
sort -t : -b -k 5,5 -k 3,3n /etc/passwd
These three commands have equivalent effect. The first specifies
that the first key's start position ignores leading blanks and the
second key is sorted numerically. The other two commands rely on
global options being inherited by sort keys that lack modifiers.
The inheritance works in this case because '-k 5b,5b' and '-k 5b,5'
are equivalent, as the location of a field-end lacking a '.C'
character position is not affected by whether initial blanks are
skipped.
• Sort a set of log files, primarily by IPv4 address and secondarily
by time stamp. If two lines' primary and secondary keys are
identical, output the lines in the same order that they were input.
The log files contain lines that look like this:
4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
Fields are separated by exactly one space. Sort IPv4 addresses
lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
because 61 is less than 129.
sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
This example cannot be done with a single 'sort' invocation, since
IPv4 address components are separated by '.' while dates come just
after a space. So it is broken down into two invocations of
'sort': the first sorts by time stamp and the second by IPv4
address. The time stamp is sorted by year, then month, then day,
and finally by hour-minute-second field, using '-k' to isolate each
field. Except for hour-minute-second there's no need to specify
the end of each key field, since the 'n' and 'M' modifiers sort
based on leading prefixes that cannot cross field boundaries. The
IPv4 addresses are sorted lexicographically. The second sort uses
'-s' so that ties in the primary key are broken by the secondary
key; the first sort uses '-s' so that the combination of the two
sorts is stable.
• Generate a tags file in case-insensitive sorted order.
find src -type f -print0 | sort -z -f | xargs -0 etags --append
The use of '-print0', '-z', and '-0' in this case means that file
names that contain blanks or other special characters are not
broken up by the sort operation.
• Use the common DSU, Decorate Sort Undecorate idiom to sort lines
according to their length.
awk '{print length, $0}' /etc/passwd | sort -n | cut -f2- -d' '
In general this technique can be used to sort data that the 'sort'
command does not support, or is inefficient at, sorting directly.
• Shuffle a list of directories, but preserve the order of files
within each directory. For instance, one could use this to
generate a music playlist in which albums are shuffled but the
songs of each album are played in order.
ls */* | sort -t / -k 1,1R -k 2,2
---------- Footnotes ----------
(1) If you use a non-POSIX locale (e.g., by setting 'LC_ALL' to
'en_US'), then 'sort' may produce output that is sorted differently than
you're accustomed to. In that case, set the 'LC_ALL' environment
variable to 'C'. Note that setting only 'LC_COLLATE' has two problems.
First, it is ineffective if 'LC_ALL' is also set. Second, it has
undefined behavior if 'LC_CTYPE' (or 'LANG', if 'LC_CTYPE' is unset) is
set to an incompatible value. For example, you get undefined behavior
if 'LC_CTYPE' is 'ja_JP.PCK' but 'LC_COLLATE' is 'en_US.UTF-8'.
(builtin command)
source: source filename [arguments]
Execute commands from a file in the current shell.
Read and execute commands from FILENAME in the current shell. The
entries in $PATH are used to find the directory containing FILENAME.
If any ARGUMENTS are supplied, they become the positional parameters
when FILENAME is executed.
Exit Status:
Returns the status of the last command executed in FILENAME; fails if
FILENAME cannot be read.
(coreutils)
'split': Split a file into pieces.
'split' creates output files containing consecutive or interleaved
sections of INPUT (standard input if none is given or INPUT is '-').
Synopsis:
split [OPTION] [INPUT [PREFIX]]
By default, 'split' puts 1000 lines of INPUT (or whatever is left
over for the last section), into each output file.
The output files' names consist of PREFIX ('x' by default) followed
by a group of characters ('aa', 'ab', ... by default), such that
concatenating the output files in traditional sorted order by file name
produces the original input file (except '-nr/N'). By default split
will initially create files with two generated suffix characters, and
will increase this width by two when the next most significant position
reaches the last character. ('yz', 'zaaa', 'zaab', ...). In this way an
arbitrary number of output files are supported, which sort as described
above, even in the presence of an '--additional-suffix' option. If the
'-a' option is specified and the output file names are exhausted,
'split' reports an error without deleting the output files that it did
create.
The program accepts the following options. Also see *note Common
options::.
'-l LINES'
'--lines=LINES'
Put LINES lines of INPUT into each output file.
For compatibility 'split' also supports an obsolete option syntax
'-LINES'. New scripts should use '-l LINES' instead.
'-b SIZE'
'--bytes=SIZE'
Put SIZE bytes of INPUT into each output file. SIZE may be, or may
be an integer optionally followed by, one of the following
multiplicative suffixes:
'b' => 512 ("blocks")
'KB' => 1000 (KiloBytes)
'K' => 1024 (KibiBytes)
'MB' => 1000*1000 (MegaBytes)
'M' => 1024*1024 (MebiBytes)
'GB' => 1000*1000*1000 (GigaBytes)
'G' => 1024*1024*1024 (GibiBytes)
and so on for 'T', 'P', 'E', 'Z', and 'Y'.
'-C SIZE'
'--line-bytes=SIZE'
Put into each output file as many complete lines of INPUT as
possible without exceeding SIZE bytes. Individual lines longer
than SIZE bytes are broken into multiple files. SIZE has the same
format as for the '--bytes' option.
'--filter=COMMAND'
With this option, rather than simply writing to each output file,
write through a pipe to the specified shell COMMAND for each output
file. COMMAND should use the $FILE environment variable, which is
set to a different output file name for each invocation of the
command. For example, imagine that you have a 1TiB compressed file
that, if uncompressed, would be too large to reside on disk, yet
you must split it into individually-compressed pieces of a more
manageable size. To do that, you might run this command:
xz -dc BIG.xz | split -b200G --filter='xz > $FILE.xz' - big-
Assuming a 10:1 compression ratio, that would create about fifty
20GiB files with names 'big-aa.xz', 'big-ab.xz', 'big-ac.xz', etc.
'-n CHUNKS'
'--number=CHUNKS'
Split INPUT to CHUNKS output files where CHUNKS may be:
N generate N files based on current size of INPUT
K/N only output Kth of N to stdout
l/N generate N files without splitting lines
l/K/N likewise but only output Kth of N to stdout
r/N like 'l' but use round robin distribution
r/K/N likewise but only output Kth of N to stdout
Any excess bytes remaining after dividing the INPUT into N chunks,
are assigned to the last chunk. Any excess bytes appearing after
the initial calculation are discarded (except when using 'r' mode).
All N files are created even if there are fewer than N lines, or
the INPUT is truncated.
For 'l' mode, chunks are approximately INPUT size / N. The INPUT
is partitioned into N equal sized portions, with the last assigned
any excess. If a line _starts_ within a partition it is written
completely to the corresponding file. Since lines are not split
even if they overlap a partition, the files written can be larger
or smaller than the partition size, and even empty if a line is so
long as to completely overlap the partition.
For 'r' mode, the size of INPUT is irrelevant, and so can be a pipe
for example.
'-a LENGTH'
'--suffix-length=LENGTH'
Use suffixes of length LENGTH. If a LENGTH of 0 is specified, this
is the same as if (any previous) '-a' was not specified, and thus
enables the default behavior, which starts the suffix length at 2,
and unless '-n' or '--numeric-suffixes=FROM' is specified, will
auto increase the length by 2 as required.
'-d'
'--numeric-suffixes[=FROM]'
Use digits in suffixes rather than lower-case letters. The
numerical suffix counts from FROM if specified, 0 otherwise. Note
specifying a FROM value also disables the default auto suffix
length expansion described above, and so you may also want to
specify '-a' to allow suffixes beyond '99'.
'--additional-suffix=SUFFIX'
Append an additional SUFFIX to output file names. SUFFIX must not
contain slash.
'-e'
'--elide-empty-files'
Suppress the generation of zero-length output files. This can
happen with the '--number' option if a file is (truncated to be)
shorter than the number requested, or if a line is so long as to
completely span a chunk. The output file sequence numbers, always
run consecutively even when this option is specified.
'-u'
'--unbuffered'
Immediately copy input to output in '--number r/...' mode, which is a
much slower mode of operation.
'--verbose'
Write a diagnostic just before each output file is opened.
An exit status of zero indicates success, and a nonzero value
indicates failure.
Here are a few examples to illustrate how the '--number' ('-n')
option works:
Notice how, by default, one line may be split onto two or more:
$ seq -w 6 10 > k; split -n3 k; head xa?
==> xaa <==
06
07
==> xab <==
08
0
==> xac <==
9
10
Use the "l/" modifier to suppress that:
$ seq -w 6 10 > k; split -nl/3 k; head xa?
==> xaa <==
06
07
==> xab <==
08
09
==> xac <==
10
Use the "r/" modifier to distribute lines in a round-robin fashion:
$ seq -w 6 10 > k; split -nr/3 k; head xa?
==> xaa <==
06
09
==> xab <==
07
10
==> xac <==
08
You can also extract just the Kth chunk. This extracts and prints
just the 7th "chunk" of 33:
$ seq 100 > k; split -nl/7/33 k
20
21
22
(coreutils)
'stat': Report file or file system status
'stat' displays information about the specified file(s). Synopsis:
stat [OPTION]... [FILE]...
With no option, 'stat' reports all information about the given files.
But it also can be used to report the information of the file systems
the given files are located on. If the files are links, 'stat' can also
give information about the files the links point to.
Due to shell aliases and built-in 'stat' functions, using an
unadorned 'stat' interactively or in a script may get you different
functionality than that described here. Invoke it via 'env' (i.e., 'env
stat ...') to avoid interference from the shell.
'-L'
'--dereference'
Change how 'stat' treats symbolic links. With this option, 'stat'
acts on the file referenced by each symbolic link argument.
Without it, 'stat' acts on any symbolic link argument directly.
'-f'
'--file-system'
Report information about the file systems where the given files are
located instead of information about the files themselves. This
option implies the '-L' option.
'-c'
'--format=FORMAT'
Use FORMAT rather than the default format. FORMAT is automatically
newline-terminated, so running a command like the following with
two or more FILE operands produces a line of output for each
operand:
$ stat --format=%d:%i / /usr
2050:2
2057:2
'--printf=FORMAT'
Use FORMAT rather than the default format. Like '--format', but
interpret backslash escapes, and do not output a mandatory trailing
newline. If you want a newline, include '\n' in the FORMAT.
Here's how you would use '--printf' to print the device and inode
numbers of '/' and '/usr':
$ stat --printf='%d:%i\n' / /usr
2050:2
2057:2
'-t'
'--terse'
Print the information in terse form, suitable for parsing by other
programs.
The valid FORMAT directives for files with '--format' and '--printf'
are:
• %a - Access rights in octal
• %A - Access rights in human readable form
• %b - Number of blocks allocated (see '%B')
• %B - The size in bytes of each block reported by '%b'
• %C - The SELinux security context of a file, if available
• %d - Device number in decimal
• %D - Device number in hex
• %f - Raw mode in hex
• %F - File type
• %g - Group ID of owner
• %G - Group name of owner
• %h - Number of hard links
• %i - Inode number
• %m - Mount point (See note below)
• %n - File name
• %N - Quoted file name with dereference if symbolic link
• %o - Optimal I/O transfer size hint
• %s - Total size, in bytes
• %t - Major device type in hex (see below)
• %T - Minor device type in hex (see below)
• %u - User ID of owner
• %U - User name of owner
• %w - Time of file birth, or '-' if unknown
• %W - Time of file birth as seconds since Epoch, or '0'
• %x - Time of last access
• %X - Time of last access as seconds since Epoch
• %y - Time of last data modification
• %Y - Time of last data modification as seconds since Epoch
• %z - Time of last status change
• %Z - Time of last status change as seconds since Epoch
The '%t' and '%T' formats operate on the st_rdev member of the
stat(2) structure, and are only defined for character and block special
files. On some systems or file types, st_rdev may be used to represent
other quantities.
The '%W', '%X', '%Y', and '%Z' formats accept a precision preceded by
a period to specify the number of digits to print after the decimal
point. For example, '%.3X' outputs the last access time to millisecond
precision. If a period is given but no precision, 'stat' uses 9 digits,
so '%.X' is equivalent to '%.9X'. When discarding excess precision,
time stamps are truncated toward minus infinity.
zero pad:
$ stat -c '[%015Y]' /usr
[000001288929712]
space align:
$ stat -c '[%15Y]' /usr
[ 1288929712]
$ stat -c '[%-15Y]' /usr
[1288929712 ]
precision:
$ stat -c '[%.3Y]' /usr
[1288929712.114]
$ stat -c '[%.Y]' /usr
[1288929712.114951834]
The mount point printed by '%m' is similar to that output by 'df',
except that:
• stat does not dereference symlinks by default (unless '-L' is
specified)
• stat does not search for specified device nodes in the file system
list, instead operating on them directly
• stat outputs the alias for a bind mounted file, rather than the
initial mount point of its backing device. One can recursively
call stat until there is no change in output, to get the current
base mount point
When listing file system information ('--file-system' ('-f')), you
must use a different set of FORMAT directives:
• %a - Free blocks available to non-super-user
• %b - Total data blocks in file system
• %c - Total file nodes in file system
• %d - Free file nodes in file system
• %f - Free blocks in file system
• %i - File System ID in hex
• %l - Maximum length of file names
• %n - File name
• %s - Block size (for faster transfers)
• %S - Fundamental block size (for block counts)
• %t - Type in hex
• %T - Type in human readable form
Time stamps are listed according to the time zone rules specified by
the 'TZ' environment variable, or by the system default rules if 'TZ' is
not set. *Note Specifying the Time Zone with 'TZ': (libc)TZ Variable.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'stdbuf': Run a command with modified I/O stream buffering
'stdbuf' allows one to modify the buffering operations of the three
standard I/O streams associated with a program. Synopsis:
stdbuf OPTION... COMMAND
COMMAND must start with the name of a program that
1. uses the ISO C 'FILE' streams for input/output (note the programs
'dd' and 'cat' don't do that),
2. does not adjust the buffering of its standard streams (note the
program 'tee' is not in this category).
Any additional ARGs are passed as additional arguments to the
COMMAND.
The program accepts the following options. Also see *note Common
options::.
'-i MODE'
'--input=MODE'
Adjust the standard input stream buffering.
'-o MODE'
'--output=MODE'
Adjust the standard output stream buffering.
'-e MODE'
'--error=MODE'
Adjust the standard error stream buffering.
The MODE can be specified as follows:
'L'
Set the stream to line buffered mode. In this mode data is
coalesced until a newline is output or input is read from any
stream attached to a terminal device. This option is invalid with
standard input.
'0'
Disable buffering of the selected stream. In this mode, data is
output immediately and only the amount of data requested is read
from input. Note the difference in function for input and output.
Disabling buffering for input will not influence the responsiveness
or blocking behavior of the stream input functions. For example
'fread' will still block until 'EOF' or error, even if the
underlying 'read' returns less data than requested.
'SIZE'
Specify the size of the buffer to use in fully buffered mode. SIZE
may be, or may be an integer optionally followed by, one of the
following multiplicative suffixes:
'KB' => 1000 (KiloBytes)
'K' => 1024 (KibiBytes)
'MB' => 1000*1000 (MegaBytes)
'M' => 1024*1024 (MebiBytes)
'GB' => 1000*1000*1000 (GigaBytes)
'G' => 1024*1024*1024 (GibiBytes)
and so on for 'T', 'P', 'E', 'Z', and 'Y'.
Exit status:
125 if 'stdbuf' itself fails
126 if COMMAND is found but cannot be invoked
127 if COMMAND cannot be found
the exit status of COMMAND otherwise
(coreutils)
'stty': Print or change terminal characteristics
'stty' prints or changes terminal characteristics, such as baud rate.
Synopses:
stty [OPTION] [SETTING]...
stty [OPTION]
If given no line settings, 'stty' prints the baud rate, line
discipline number (on systems that support it), and line settings that
have been changed from the values set by 'stty sane'. By default, mode
reading and setting are performed on the tty line connected to standard
input, although this can be modified by the '--file' option.
'stty' accepts many non-option arguments that change aspects of the
terminal line operation, as described below.
The program accepts the following options. Also see *note Common
options::.
'-a'
'--all'
Print all current settings in human-readable form. This option may
not be used in combination with any line settings.
'-F DEVICE'
'--file=DEVICE'
Set the line opened by the file name specified in DEVICE instead of
the tty line connected to standard input. This option is necessary
because opening a POSIX tty requires use of the 'O_NONDELAY' flag
to prevent a POSIX tty from blocking until the carrier detect line
is high if the 'clocal' flag is not set. Hence, it is not always
possible to allow the shell to open the device in the traditional
manner.
'-g'
'--save'
Print all current settings in a form that can be used as an
argument to another 'stty' command to restore the current settings.
This option may not be used in combination with any line settings.
Many settings can be turned off by preceding them with a '-'. Such
arguments are marked below with "May be negated" in their description.
The descriptions themselves refer to the positive case, that is, when
_not_ negated (unless stated otherwise, of course).
Some settings are not available on all POSIX systems, since they use
extensions. Such arguments are marked below with "Non-POSIX" in their
description. On non-POSIX systems, those or other settings also may not
be available, but it's not feasible to document all the variations: just
try it and see.
An exit status of zero indicates success, and a nonzero value
indicates failure.
* Menu:
* Control:: Control settings
* Input:: Input settings
* Output:: Output settings
* Local:: Local settings
* Combination:: Combination settings
* Characters:: Special characters
* Special:: Special settings
Control settings
----------------
Control settings:
'parenb'
Generate parity bit in output and expect parity bit in input. May
be negated.
'parodd'
Set odd parity (even if negated). May be negated.
'cmspar'
Use "stick" (mark/space) parity. If parodd is set, the parity bit
is always 1; if parodd is not set, the parity bit is always zero.
Non-POSIX. May be negated.
'cs5'
'cs6'
'cs7'
'cs8'
Set character size to 5, 6, 7, or 8 bits.
'hup'
'hupcl'
Send a hangup signal when the last process closes the tty. May be
negated.
'cstopb'
Use two stop bits per character (one if negated). May be negated.
'cread'
Allow input to be received. May be negated.
'clocal'
Disable modem control signals. May be negated.
'crtscts'
Enable RTS/CTS flow control. Non-POSIX. May be negated.
'cdtrdsr'
Enable DTR/DSR flow control. Non-POSIX. May be negated.
Input settings
--------------
These settings control operations on data received from the terminal.
'ignbrk'
Ignore break characters. May be negated.
'brkint'
Make breaks cause an interrupt signal. May be negated.
'ignpar'
Ignore characters with parity errors. May be negated.
'parmrk'
Mark parity errors (with a 255-0-character sequence). May be
negated.
'inpck'
Enable input parity checking. May be negated.
'istrip'
Clear high (8th) bit of input characters. May be negated.
'inlcr'
Translate newline to carriage return. May be negated.
'igncr'
Ignore carriage return. May be negated.
'icrnl'
Translate carriage return to newline. May be negated.
'iutf8'
Assume input characters are UTF-8 encoded. May be negated.
'ixon'
Enable XON/XOFF flow control (that is, 'Ctrl-S'/'Ctrl-Q'). May be
negated.
'ixoff'
'tandem'
Enable sending of 'stop' character when the system input buffer is
almost full, and 'start' character when it becomes almost empty
again. May be negated.
'iuclc'
Translate uppercase characters to lowercase. Non-POSIX. May be
negated. Note ilcuc is not implemented, as one would not be able
to issue almost any (lowercase) Unix command, after invoking it.
'ixany'
Allow any character to restart output (only the start character if
negated). Non-POSIX. May be negated.
'imaxbel'
Enable beeping and not flushing input buffer if a character arrives
when the input buffer is full. Non-POSIX. May be negated.
Output settings
---------------
These settings control operations on data sent to the terminal.
'opost'
Postprocess output. May be negated.
'olcuc'
Translate lowercase characters to uppercase. Non-POSIX. May be
negated. (Note ouclc is not currently implemented.)
'ocrnl'
Translate carriage return to newline. Non-POSIX. May be negated.
'onlcr'
Translate newline to carriage return-newline. Non-POSIX. May be
negated.
'onocr'
Do not print carriage returns in the first column. Non-POSIX. May
be negated.
'onlret'
Newline performs a carriage return. Non-POSIX. May be negated.
'ofill'
Use fill (padding) characters instead of timing for delays.
Non-POSIX. May be negated.
'ofdel'
Use ASCII DEL characters for fill instead of ASCII NUL characters.
Non-POSIX. May be negated.
'nl1'
'nl0'
Newline delay style. Non-POSIX.
'cr3'
'cr2'
'cr1'
'cr0'
Carriage return delay style. Non-POSIX.
'tab3'
'tab2'
'tab1'
'tab0'
Horizontal tab delay style. Non-POSIX.
'bs1'
'bs0'
Backspace delay style. Non-POSIX.
'vt1'
'vt0'
Vertical tab delay style. Non-POSIX.
'ff1'
'ff0'
Form feed delay style. Non-POSIX.
Local settings
--------------
'isig'
Enable 'interrupt', 'quit', and 'suspend' special characters. May
be negated.
'icanon'
Enable 'erase', 'kill', 'werase', and 'rprnt' special characters.
May be negated.
'iexten'
Enable non-POSIX special characters. May be negated.
'echo'
Echo input characters. May be negated.
'echoe'
'crterase'
Echo 'erase' characters as backspace-space-backspace. May be
negated.
'echok'
Echo a newline after a 'kill' character. May be negated.
'echonl'
Echo newline even if not echoing other characters. May be negated.
'noflsh'
Disable flushing after 'interrupt' and 'quit' special characters.
May be negated.
'xcase'
Enable input and output of uppercase characters by preceding their
lowercase equivalents with '\', when 'icanon' is set. Non-POSIX.
May be negated.
'tostop'
Stop background jobs that try to write to the terminal. Non-POSIX.
May be negated.
'echoprt'
'prterase'
Echo erased characters backward, between '\' and '/'. Non-POSIX.
May be negated.
'echoctl'
'ctlecho'
Echo control characters in hat notation ('^C') instead of
literally. Non-POSIX. May be negated.
'echoke'
'crtkill'
Echo the 'kill' special character by erasing each character on the
line as indicated by the 'echoprt' and 'echoe' settings, instead of
by the 'echoctl' and 'echok' settings. Non-POSIX. May be negated.
Combination settings
--------------------
Combination settings:
'evenp'
'parity'
Same as 'parenb -parodd cs7'. May be negated. If negated, same as
'-parenb cs8'.
'oddp'
Same as 'parenb parodd cs7'. May be negated. If negated, same as
'-parenb cs8'.
'nl'
Same as '-icrnl -onlcr'. May be negated. If negated, same as
'icrnl -inlcr -igncr onlcr -ocrnl -onlret'.
'ek'
Reset the 'erase' and 'kill' special characters to their default
values.
'sane'
Same as:
cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
-iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
-onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
ff0 isig icanon iexten echo echoe echok -echonl
-noflsh -xcase -tostop -echoprt echoctl echoke
and also sets all special characters to their default values.
'cooked'
Same as 'brkint ignpar istrip icrnl ixon opost isig icanon', plus
sets the 'eof' and 'eol' characters to their default values if they
are the same as the 'min' and 'time' characters. May be negated.
If negated, same as 'raw'.
'raw'
Same as:
-ignbrk -brkint -ignpar -parmrk -inpck -istrip
-inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
-imaxbel -opost -isig -icanon -xcase min 1 time 0
May be negated. If negated, same as 'cooked'.
'cbreak'
Same as '-icanon'. May be negated. If negated, same as 'icanon'.
'pass8'
Same as '-parenb -istrip cs8'. May be negated. If negated, same
as 'parenb istrip cs7'.
'litout'
Same as '-parenb -istrip -opost cs8'. May be negated. If negated,
same as 'parenb istrip opost cs7'.
'decctlq'
Same as '-ixany'. Non-POSIX. May be negated.
'tabs'
Same as 'tab0'. Non-POSIX. May be negated. If negated, same as
'tab3'.
'lcase'
'LCASE'
Same as 'xcase iuclc olcuc'. Non-POSIX. May be negated. (Used
for terminals with uppercase characters only.)
'crt'
Same as 'echoe echoctl echoke'.
'dec'
Same as 'echoe echoctl echoke -ixany intr ^C erase ^? kill C-u'.
Special characters
------------------
The special characters' default values vary from system to system. They
are set with the syntax 'name value', where the names are listed below
and the value can be given either literally, in hat notation ('^C'), or
as an integer which may start with '0x' to indicate hexadecimal, '0' to
indicate octal, or any other digit to indicate decimal.
For GNU stty, giving a value of '^-' or 'undef' disables that special
character. (This is incompatible with Ultrix 'stty', which uses a value
of 'u' to disable a special character. GNU 'stty' treats a value 'u'
like any other, namely to set that special character to <U>.)
'intr'
Send an interrupt signal.
'quit'
Send a quit signal.
'erase'
Erase the last character typed.
'kill'
Erase the current line.
'eof'
Send an end of file (terminate the input).
'eol'
End the line.
'eol2'
Alternate character to end the line. Non-POSIX.
'swtch'
Switch to a different shell layer. Non-POSIX.
'start'
Restart the output after stopping it.
'stop'
Stop the output.
'susp'
Send a terminal stop signal.
'dsusp'
Send a terminal stop signal after flushing the input. Non-POSIX.
'rprnt'
Redraw the current line. Non-POSIX.
'werase'
Erase the last word typed. Non-POSIX.
'lnext'
Enter the next character typed literally, even if it is a special
character. Non-POSIX.
Special settings
----------------
'min N'
Set the minimum number of characters that will satisfy a read until
the time value has expired, when '-icanon' is set.
'time N'
Set the number of tenths of a second before reads time out if the
minimum number of characters have not been read, when '-icanon' is
set.
'ispeed N'
Set the input speed to N.
'ospeed N'
Set the output speed to N.
'rows N'
Tell the tty kernel driver that the terminal has N rows.
Non-POSIX.
'cols N'
'columns N'
Tell the kernel that the terminal has N columns. Non-POSIX.
'size'
Print the number of rows and columns that the kernel thinks the
terminal has. (Systems that don't support rows and columns in the
kernel typically use the environment variables 'LINES' and
'COLUMNS' instead; however, GNU 'stty' does not know anything about
them.) Non-POSIX.
'line N'
Use line discipline N. Non-POSIX.
'speed'
Print the terminal speed.
'N'
Set the input and output speeds to N. N can be one of: 0 50 75 110
134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200 38400
'exta' 'extb'. 'exta' is the same as 19200; 'extb' is the same as
38400. Many systems, including GNU/Linux, support higher speeds.
The 'stty' command includes support for speeds of 57600, 115200,
230400, 460800, 500000, 576000, 921600, 1000000, 1152000, 1500000,
2000000, 2500000, 3000000, 3500000, or 4000000 where the system
supports these. 0 hangs up the line if '-clocal' is set.
(coreutils)
'sum': Print checksum and block counts
'sum' computes a 16-bit checksum for each given FILE, or standard input
if none are given or for a FILE of '-'. Synopsis:
sum [OPTION]... [FILE]...
'sum' prints the checksum for each FILE followed by the number of
blocks in the file (rounded up). If more than one FILE is given, file
names are also printed (by default). (With the '--sysv' option,
corresponding file names are printed when there is at least one file
argument.)
By default, GNU 'sum' computes checksums using an algorithm
compatible with BSD 'sum' and prints file sizes in units of 1024-byte
blocks.
The program accepts the following options. Also see *note Common
options::.
'-r'
Use the default (BSD compatible) algorithm. This option is
included for compatibility with the System V 'sum'. Unless '-s'
was also given, it has no effect.
'-s'
'--sysv'
Compute checksums using an algorithm compatible with System V
'sum''s default, and print file sizes in units of 512-byte blocks.
'sum' is provided for compatibility; the 'cksum' program (see next
section) is preferable in new applications.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(builtin command)
suspend: suspend [-f]
Suspend shell execution.
Suspend the execution of this shell until it receives a SIGCONT signal.
Unless forced, login shells cannot be suspended.
Options:
-f force the suspend, even if the shell is a login shell
Exit Status:
Returns success unless job control is not enabled or an error occurs.
(coreutils)
'sync': Synchronize data on disk with memory 'sync' writes any data buffered in memory out to disk. This can include (but is not limited to) modified superblocks, modified inodes, and delayed reads and writes. This must be implemented by the kernel; The 'sync' program does nothing but exercise the 'sync' system call. The kernel keeps data in memory to avoid doing (relatively slow) disk reads and writes. This improves performance, but if the computer crashes, data may be lost or the file system corrupted as a result. The 'sync' command ensures everything in memory is written to disk. Any arguments are ignored, except for a lone '--help' or '--version' (*note Common options::). An exit status of zero indicates success, and a nonzero value indicates failure.
(coreutils)
'tac': Concatenate and write files in reverse
'tac' copies each FILE ('-' means standard input), or standard input if
none are given, to standard output, reversing the records (lines by
default) in each separately. Synopsis:
tac [OPTION]... [FILE]...
"Records" are separated by instances of a string (newline by
default). By default, this separator string is attached to the end of
the record that it follows in the file.
The program accepts the following options. Also see *note Common
options::.
'-b'
'--before'
The separator is attached to the beginning of the record that it
precedes in the file.
'-r'
'--regex'
Treat the separator string as a regular expression.
'-s SEPARATOR'
'--separator=SEPARATOR'
Use SEPARATOR as the record separator, instead of newline.
On systems like MS-DOS that distinguish between text and binary
files, 'tac' reads and writes in binary mode.
An exit status of zero indicates success, and a nonzero value
indicates failure.
Example:
# Reverse a file character by character.
tac -r -s 'x\|[^x]'
(coreutils)
'tail': Output the last part of files
'tail' prints the last part (10 lines by default) of each FILE; it reads
from standard input if no files are given or when given a FILE of '-'.
Synopsis:
tail [OPTION]... [FILE]...
If more than one FILE is specified, 'tail' prints a one-line header
consisting of:
==> FILE NAME <==
before the output for each FILE.
GNU 'tail' can output any amount of data (some other versions of
'tail' cannot). It also has no '-r' option (print in reverse), since
reversing a file is really a different job from printing the end of a
file; BSD 'tail' (which is the one with '-r') can only reverse files
that are at most as large as its buffer, which is typically 32 KiB. A
more reliable and versatile way to reverse files is the GNU 'tac'
command.
The program accepts the following options. Also see *note Common
options::.
'-c K'
'--bytes=K'
Output the last K bytes, instead of final lines. However, if K
starts with a '+', start printing with the Kth byte from the start
of each file, instead of from the end. K may be, or may be an
integer optionally followed by, one of the following multiplicative
suffixes:
'b' => 512 ("blocks")
'KB' => 1000 (KiloBytes)
'K' => 1024 (KibiBytes)
'MB' => 1000*1000 (MegaBytes)
'M' => 1024*1024 (MebiBytes)
'GB' => 1000*1000*1000 (GigaBytes)
'G' => 1024*1024*1024 (GibiBytes)
and so on for 'T', 'P', 'E', 'Z', and 'Y'.
'-f'
'--follow[=HOW]'
Loop forever trying to read more characters at the end of the file,
presumably because the file is growing. If more than one file is
given, 'tail' prints a header whenever it gets output from a
different file, to indicate which file that output is from.
There are two ways to specify how you'd like to track files with
this option, but that difference is noticeable only when a followed
file is removed or renamed. If you'd like to continue to track the
end of a growing file even after it has been unlinked, use
'--follow=descriptor'. This is the default behavior, but it is not
useful if you're tracking a log file that may be rotated (removed
or renamed, then reopened). In that case, use '--follow=name' to
track the named file, perhaps by reopening it periodically to see
if it has been removed and recreated by some other program. Note
that the inotify-based implementation handles this case without the
need for any periodic reopening.
No matter which method you use, if the tracked file is determined
to have shrunk, 'tail' prints a message saying the file has been
truncated and resumes tracking the end of the file from the
newly-determined endpoint.
When a file is removed, 'tail''s behavior depends on whether it is
following the name or the descriptor. When following by name, tail
can detect that a file has been removed and gives a message to that
effect, and if '--retry' has been specified it will continue
checking periodically to see if the file reappears. When following
a descriptor, tail does not detect that the file has been unlinked
or renamed and issues no message; even though the file may no
longer be accessible via its original name, it may still be
growing.
The option values 'descriptor' and 'name' may be specified only
with the long form of the option, not with '-f'.
The '-f' option is ignored if no FILE operand is specified and
standard input is a FIFO or a pipe. Likewise, the '-f' option has
no effect for any operand specified as '-', when standard input is
a FIFO or a pipe.
With kernel inotify support, output is triggered by file changes
and is generally very prompt. Otherwise, 'tail' sleeps for one
second between checks— use '--sleep-interval=N' to change that
default—which can make the output appear slightly less responsive
or bursty. When using tail without inotify support, you can make
it more responsive by using a sub-second sleep interval, e.g., via
an alias like this:
alias tail='tail -s.1'
'-F'
This option is the same as '--follow=name --retry'. That is, tail
will attempt to reopen a file when it is removed. Should this
fail, tail will keep trying until it becomes accessible again.
'--retry'
Indefinitely try to open the specified file. This option is useful
mainly when following (and otherwise issues a warning).
When following by file descriptor (i.e., with
'--follow=descriptor'), this option only affects the initial open
of the file, as after a successful open, 'tail' will start
following the file descriptor.
When following by name (i.e., with '--follow=name'), 'tail'
infinitely retries to re-open the given files until killed.
Without this option, when 'tail' encounters a file that doesn't
exist or is otherwise inaccessible, it reports that fact and never
checks it again.
'--sleep-interval=NUMBER'
Change the number of seconds to wait between iterations (the
default is 1.0). During one iteration, every specified file is
checked to see if it has changed size. Historical implementations
of 'tail' have required that NUMBER be an integer. However, GNU
'tail' accepts an arbitrary floating point number. *Note Floating
point::. When 'tail' uses inotify, this polling-related option is
usually ignored. However, if you also specify '--pid=P', 'tail'
checks whether process P is alive at least every NUMBER seconds.
'--pid=PID'
When following by name or by descriptor, you may specify the
process ID, PID, of the sole writer of all FILE arguments. Then,
shortly after that process terminates, tail will also terminate.
This will work properly only if the writer and the tailing process
are running on the same machine. For example, to save the output
of a build in a file and to watch the file grow, if you invoke
'make' and 'tail' like this then the tail process will stop when
your build completes. Without this option, you would have had to
kill the 'tail -f' process yourself.
$ make >& makerr & tail --pid=$! -f makerr
If you specify a PID that is not in use or that does not correspond
to the process that is writing to the tailed files, then 'tail' may
terminate long before any FILEs stop growing or it may not
terminate until long after the real writer has terminated. Note
that '--pid' cannot be supported on some systems; 'tail' will print
a warning if this is the case.
'--max-unchanged-stats=N'
When tailing a file by name, if there have been N (default n=5)
consecutive iterations for which the file has not changed, then
'open'/'fstat' the file to determine if that file name is still
associated with the same device/inode-number pair as before. When
following a log file that is rotated, this is approximately the
number of seconds between when tail prints the last pre-rotation
lines and when it prints the lines that have accumulated in the new
log file. This option is meaningful only when polling (i.e.,
without inotify) and when following by name.
'-n K'
'--lines=K'
Output the last K lines. However, if K starts with a '+', start
printing with the Kth line from the start of each file, instead of
from the end. Size multiplier suffixes are the same as with the
'-c' option.
'-q'
'--quiet'
'--silent'
Never print file name headers.
'-v'
'--verbose'
Always print file name headers.
For compatibility 'tail' also supports an obsolete usage 'tail
-[COUNT][bcl][f] [FILE]', which is recognized only if it does not
conflict with the usage described above. This obsolete form uses
exactly one option and at most one file. In the option, COUNT is an
optional decimal number optionally followed by a size letter ('b', 'c',
'l') to mean count by 512-byte blocks, bytes, or lines, optionally
followed by 'f' which has the same meaning as '-f'.
On older systems, the leading '-' can be replaced by '+' in the
obsolete option syntax with the same meaning as in counts, and obsolete
usage overrides normal usage when the two conflict. This obsolete
behavior can be enabled or disabled with the '_POSIX2_VERSION'
environment variable (*note Standards conformance::).
Scripts intended for use on standard hosts should avoid obsolete
syntax and should use '-c COUNT[b]', '-n COUNT', and/or '-f' instead.
If your script must also run on hosts that support only the obsolete
syntax, you can often rewrite it to avoid problematic usages, e.g., by
using 'sed -n '$p'' rather than 'tail -1'. If that's not possible, the
script can use a test like 'if tail -c +1 </dev/null >/dev/null 2>&1;
then ...' to decide which syntax to use.
Even if your script assumes the standard behavior, you should still
beware usages whose behaviors differ depending on the POSIX version.
For example, avoid 'tail - main.c', since it might be interpreted as
either 'tail main.c' or as 'tail -- - main.c'; avoid 'tail -c 4', since
it might mean either 'tail -c4' or 'tail -c 10 4'; and avoid 'tail +4',
since it might mean either 'tail ./+4' or 'tail -n +4'.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'tee': Redirect output to multiple files or processes
The 'tee' command copies standard input to standard output and also to
any files given as arguments. This is useful when you want not only to
send some data down a pipe, but also to save a copy. Synopsis:
tee [OPTION]... [FILE]...
If a file being written to does not already exist, it is created. If
a file being written to already exists, the data it previously contained
is overwritten unless the '-a' option is used.
A FILE of '-' causes 'tee' to send another copy of input to standard
output, but this is typically not that useful as the copies are
interleaved.
The program accepts the following options. Also see *note Common
options::.
'-a'
'--append'
Append standard input to the given files rather than overwriting
them.
'-i'
'--ignore-interrupts'
Ignore interrupt signals.
The 'tee' command is useful when you happen to be transferring a
large amount of data and also want to summarize that data without
reading it a second time. For example, when you are downloading a DVD
image, you often want to verify its signature or checksum right away.
The inefficient way to do it is simply:
wget http://example.com/some.iso && sha1sum some.iso
One problem with the above is that it makes you wait for the download
to complete before starting the time-consuming SHA1 computation.
Perhaps even more importantly, the above requires reading the DVD image
a second time (the first was from the network).
The efficient way to do it is to interleave the download and SHA1
computation. Then, you'll get the checksum for free, because the entire
process parallelizes so well:
# slightly contrived, to demonstrate process substitution
wget -O - http://example.com/dvd.iso \
| tee >(sha1sum > dvd.sha1) > dvd.iso
That makes 'tee' write not just to the expected output file, but also
to a pipe running 'sha1sum' and saving the final checksum in a file
named 'dvd.sha1'.
Note, however, that this example relies on a feature of modern shells
called "process substitution" (the '>(command)' syntax, above; *Note
Process Substitution: (bash)Process Substitution.), so it works with
'zsh', 'bash', and 'ksh', but not with '/bin/sh'. So if you write code
like this in a shell script, be sure to start the script with
'#!/bin/bash'.
Since the above example writes to one file and one process, a more
conventional and portable use of 'tee' is even better:
wget -O - http://example.com/dvd.iso \
| tee dvd.iso | sha1sum > dvd.sha1
You can extend this example to make 'tee' write to two processes,
computing MD5 and SHA1 checksums in parallel. In this case, process
substitution is required:
wget -O - http://example.com/dvd.iso \
| tee >(sha1sum > dvd.sha1) \
>(md5sum > dvd.md5) \
> dvd.iso
This technique is also useful when you want to make a _compressed_
copy of the contents of a pipe. Consider a tool to graphically
summarize disk usage data from 'du -ak'. For a large hierarchy, 'du
-ak' can run for a long time, and can easily produce terabytes of data,
so you won't want to rerun the command unnecessarily. Nor will you want
to save the uncompressed output.
Doing it the inefficient way, you can't even start the GUI until
after you've compressed all of the 'du' output:
du -ak | gzip -9 > /tmp/du.gz
gzip -d /tmp/du.gz | xdiskusage -a
With 'tee' and process substitution, you start the GUI right away and
eliminate the decompression completely:
du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
Finally, if you regularly create more than one type of compressed
tarball at once, for example when 'make dist' creates both
'gzip'-compressed and 'bzip2'-compressed tarballs, there may be a better
way. Typical 'automake'-generated 'Makefile' rules create the two
compressed tar archives with commands in sequence, like this (slightly
simplified):
tardir=your-pkg-M.N
tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
However, if the hierarchy you are archiving and compressing is larger
than a couple megabytes, and especially if you are using a
multi-processor system with plenty of memory, then you can do much
better by reading the directory contents only once and running the
compression programs in parallel:
tardir=your-pkg-M.N
tar chof - "$tardir" \
| tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
| bzip2 -9 -c > your-pkg-M.N.tar.bz2
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'test': Check file types and compare values
'test' returns a status of 0 (true) or 1 (false) depending on the
evaluation of the conditional expression EXPR. Each part of the
expression must be a separate argument.
'test' has file status checks, string operators, and numeric
comparison operators.
'test' has an alternate form that uses opening and closing square
brackets instead a leading 'test'. For example, instead of 'test -d /',
you can write '[ -d / ]'. The square brackets must be separate
arguments; for example, '[-d /]' does not have the desired effect.
Since 'test EXPR' and '[ EXPR ]' have the same meaning, only the former
form is discussed below.
Synopses:
test EXPRESSION
test
[ EXPRESSION ]
[ ]
[ OPTION
Due to shell aliases and built-in 'test' functions, using an
unadorned 'test' interactively or in a script may get you different
functionality than that described here. Invoke it via 'env' (i.e., 'env
test ...') to avoid interference from the shell.
If EXPRESSION is omitted, 'test' returns false. If EXPRESSION is a
single argument, 'test' returns false if the argument is null and true
otherwise. The argument can be any string, including strings like '-d',
'-1', '--', '--help', and '--version' that most other programs would
treat as options. To get help and version information, invoke the
commands '[ --help' and '[ --version', without the usual closing
brackets. *Note Common options::.
Exit status:
0 if the expression is true,
1 if the expression is false,
2 if an error occurred.
* Menu:
* File type tests:: -[bcdfhLpSt]
* Access permission tests:: -[gkruwxOG]
* File characteristic tests:: -e -s -nt -ot -ef
* String tests:: -z -n = == !=
* Numeric tests:: -eq -ne -lt -le -gt -ge
* Connectives for test:: ! -a -o
File type tests
---------------
These options test for particular types of files. (Everything's a file,
but not all files are the same!)
'-b FILE'
True if FILE exists and is a block special device.
'-c FILE'
True if FILE exists and is a character special device.
'-d FILE'
True if FILE exists and is a directory.
'-f FILE'
True if FILE exists and is a regular file.
'-h FILE'
'-L FILE'
True if FILE exists and is a symbolic link. Unlike all other
file-related tests, this test does not dereference FILE if it is a
symbolic link.
'-p FILE'
True if FILE exists and is a named pipe.
'-S FILE'
True if FILE exists and is a socket.
'-t FD'
True if FD is a file descriptor that is associated with a terminal.
Access permission tests
-----------------------
These options test for particular access permissions.
'-g FILE'
True if FILE exists and has its set-group-ID bit set.
'-k FILE'
True if FILE exists and has its "sticky" bit set.
'-r FILE'
True if FILE exists and read permission is granted.
'-u FILE'
True if FILE exists and has its set-user-ID bit set.
'-w FILE'
True if FILE exists and write permission is granted.
'-x FILE'
True if FILE exists and execute permission is granted (or search
permission, if it is a directory).
'-O FILE'
True if FILE exists and is owned by the current effective user ID.
'-G FILE'
True if FILE exists and is owned by the current effective group ID.
File characteristic tests
-------------------------
These options test other file characteristics.
'-e FILE'
True if FILE exists.
'-s FILE'
True if FILE exists and has a size greater than zero.
'FILE1 -nt FILE2'
True if FILE1 is newer (according to modification date) than FILE2,
or if FILE1 exists and FILE2 does not.
'FILE1 -ot FILE2'
True if FILE1 is older (according to modification date) than FILE2,
or if FILE2 exists and FILE1 does not.
'FILE1 -ef FILE2'
True if FILE1 and FILE2 have the same device and inode numbers,
i.e., if they are hard links to each other.
String tests
------------
These options test string characteristics. You may need to quote STRING
arguments for the shell. For example:
test -n "$V"
The quotes here prevent the wrong arguments from being passed to
'test' if '$V' is empty or contains special characters.
'-z STRING'
True if the length of STRING is zero.
'-n STRING'
'STRING'
True if the length of STRING is nonzero.
'STRING1 = STRING2'
True if the strings are equal.
'STRING1 == STRING2'
True if the strings are equal (synonym for =).
'STRING1 != STRING2'
True if the strings are not equal.
Numeric tests
-------------
Numeric relational operators. The arguments must be entirely numeric
(possibly negative), or the special expression '-l STRING', which
evaluates to the length of STRING.
'ARG1 -eq ARG2'
'ARG1 -ne ARG2'
'ARG1 -lt ARG2'
'ARG1 -le ARG2'
'ARG1 -gt ARG2'
'ARG1 -ge ARG2'
These arithmetic binary operators return true if ARG1 is equal,
not-equal, less-than, less-than-or-equal, greater-than, or
greater-than-or-equal than ARG2, respectively.
For example:
test -1 -gt -2 && echo yes
⇒ yes
test -l abc -gt 1 && echo yes
⇒ yes
test 0x100 -eq 1
error→ test: integer expression expected before -eq
Connectives for 'test'
----------------------
The usual logical connectives.
'! EXPR'
True if EXPR is false.
'EXPR1 -a EXPR2'
True if both EXPR1 and EXPR2 are true.
'EXPR1 -o EXPR2'
True if either EXPR1 or EXPR2 is true.
(coreutils)
'test': Check file types and compare values
'test' returns a status of 0 (true) or 1 (false) depending on the
evaluation of the conditional expression EXPR. Each part of the
expression must be a separate argument.
'test' has file status checks, string operators, and numeric
comparison operators.
'test' has an alternate form that uses opening and closing square
brackets instead a leading 'test'. For example, instead of 'test -d /',
you can write '[ -d / ]'. The square brackets must be separate
arguments; for example, '[-d /]' does not have the desired effect.
Since 'test EXPR' and '[ EXPR ]' have the same meaning, only the former
form is discussed below.
Synopses:
test EXPRESSION
test
[ EXPRESSION ]
[ ]
[ OPTION
Due to shell aliases and built-in 'test' functions, using an
unadorned 'test' interactively or in a script may get you different
functionality than that described here. Invoke it via 'env' (i.e., 'env
test ...') to avoid interference from the shell.
If EXPRESSION is omitted, 'test' returns false. If EXPRESSION is a
single argument, 'test' returns false if the argument is null and true
otherwise. The argument can be any string, including strings like '-d',
'-1', '--', '--help', and '--version' that most other programs would
treat as options. To get help and version information, invoke the
commands '[ --help' and '[ --version', without the usual closing
brackets. *Note Common options::.
Exit status:
0 if the expression is true,
1 if the expression is false,
2 if an error occurred.
* Menu:
* File type tests:: -[bcdfhLpSt]
* Access permission tests:: -[gkruwxOG]
* File characteristic tests:: -e -s -nt -ot -ef
* String tests:: -z -n = == !=
* Numeric tests:: -eq -ne -lt -le -gt -ge
* Connectives for test:: ! -a -o
File type tests
---------------
These options test for particular types of files. (Everything's a file,
but not all files are the same!)
'-b FILE'
True if FILE exists and is a block special device.
'-c FILE'
True if FILE exists and is a character special device.
'-d FILE'
True if FILE exists and is a directory.
'-f FILE'
True if FILE exists and is a regular file.
'-h FILE'
'-L FILE'
True if FILE exists and is a symbolic link. Unlike all other
file-related tests, this test does not dereference FILE if it is a
symbolic link.
'-p FILE'
True if FILE exists and is a named pipe.
'-S FILE'
True if FILE exists and is a socket.
'-t FD'
True if FD is a file descriptor that is associated with a terminal.
Access permission tests
-----------------------
These options test for particular access permissions.
'-g FILE'
True if FILE exists and has its set-group-ID bit set.
'-k FILE'
True if FILE exists and has its "sticky" bit set.
'-r FILE'
True if FILE exists and read permission is granted.
'-u FILE'
True if FILE exists and has its set-user-ID bit set.
'-w FILE'
True if FILE exists and write permission is granted.
'-x FILE'
True if FILE exists and execute permission is granted (or search
permission, if it is a directory).
'-O FILE'
True if FILE exists and is owned by the current effective user ID.
'-G FILE'
True if FILE exists and is owned by the current effective group ID.
File characteristic tests
-------------------------
These options test other file characteristics.
'-e FILE'
True if FILE exists.
'-s FILE'
True if FILE exists and has a size greater than zero.
'FILE1 -nt FILE2'
True if FILE1 is newer (according to modification date) than FILE2,
or if FILE1 exists and FILE2 does not.
'FILE1 -ot FILE2'
True if FILE1 is older (according to modification date) than FILE2,
or if FILE2 exists and FILE1 does not.
'FILE1 -ef FILE2'
True if FILE1 and FILE2 have the same device and inode numbers,
i.e., if they are hard links to each other.
String tests
------------
These options test string characteristics. You may need to quote STRING
arguments for the shell. For example:
test -n "$V"
The quotes here prevent the wrong arguments from being passed to
'test' if '$V' is empty or contains special characters.
'-z STRING'
True if the length of STRING is zero.
'-n STRING'
'STRING'
True if the length of STRING is nonzero.
'STRING1 = STRING2'
True if the strings are equal.
'STRING1 == STRING2'
True if the strings are equal (synonym for =).
'STRING1 != STRING2'
True if the strings are not equal.
Numeric tests
-------------
Numeric relational operators. The arguments must be entirely numeric
(possibly negative), or the special expression '-l STRING', which
evaluates to the length of STRING.
'ARG1 -eq ARG2'
'ARG1 -ne ARG2'
'ARG1 -lt ARG2'
'ARG1 -le ARG2'
'ARG1 -gt ARG2'
'ARG1 -ge ARG2'
These arithmetic binary operators return true if ARG1 is equal,
not-equal, less-than, less-than-or-equal, greater-than, or
greater-than-or-equal than ARG2, respectively.
For example:
test -1 -gt -2 && echo yes
⇒ yes
test -l abc -gt 1 && echo yes
⇒ yes
test 0x100 -eq 1
error→ test: integer expression expected before -eq
Connectives for 'test'
-----------------------
The usual logical connectives.
'! EXPR'
True if EXPR is false.
'EXPR1 -a EXPR2'
True if both EXPR1 and EXPR2 are true.
'EXPR1 -o EXPR2'
True if either EXPR1 or EXPR2 is true.
(reserved word)
time: time [-p] pipeline
Report time consumed by pipeline's execution.
Execute PIPELINE and print a summary of the real time, user CPU time,
and system CPU time spent executing PIPELINE when it terminates.
Options:
-p print the timing summary in the portable Posix format
The value of the TIMEFORMAT variable is used as the output format.
Exit Status:
The return status is the return status of PIPELINE.
(coreutils)
'timeout': Run a command with a time limit
'timeout' runs the given COMMAND and kills it if it is still running
after the specified time interval. Synopsis:
timeout [OPTION] DURATION COMMAND [ARG]...
COMMAND must not be a special built-in utility (*note Special
built-in utilities::).
The program accepts the following options. Also see *note Common
options::. Options must precede operands.
'--preserve-status'
Return the exit status of the managed COMMAND on timeout, rather
than a specific exit status indicating a timeout. This is useful
if the managed COMMAND supports running for an indeterminite amount
of time.
'--foreground'
Don't create a separate background program group, so that the
managed COMMAND can use the foreground TTY normally. This is
needed to support timing out commands not started directly from an
interactive shell, in two situations.
1. COMMAND is interactive and needs to read from the terminal for
example
2. the user wants to support sending signals directly to COMMAND
from the terminal (like Ctrl-C for example)
Note in this mode of operation, any children of COMMAND will not be
timed out.
'-k DURATION'
'--kill-after=DURATION'
Ensure the monitored COMMAND is killed by also sending a 'KILL'
signal, after the specified DURATION. Without this option, if the
selected signal proves not to be fatal, 'timeout' does not kill the
COMMAND.
'-s SIGNAL'
'--signal=SIGNAL'
Send this SIGNAL to COMMAND on timeout, rather than the default
'TERM' signal. SIGNAL may be a name like 'HUP' or a number. *Note
Signal specifications::.
DURATION is a floating point number followed by an optional unit:
's' for seconds (the default)
'm' for minutes
'h' for hours
'd' for days
A duration of 0 disables the associated timeout. Note that the
actual timeout duration is dependent on system conditions, which should
be especially considered when specifying sub-second timeouts.
Exit status:
124 if COMMAND times out
125 if 'timeout' itself fails
126 if COMMAND is found but cannot be invoked
127 if COMMAND cannot be found
137 if COMMAND is sent the KILL(9) signal (128+9)
the exit status of COMMAND otherwise
(builtin command)
times: times
Display process times.
Prints the accumulated user and system times for the shell and all of its
child processes.
Exit Status:
Always succeeds.
(coreutils)
'touch': Change file timestamps
'touch' changes the access and/or modification times of the specified
files. Synopsis:
touch [OPTION]... FILE...
Any FILE argument that does not exist is created empty, unless option
'--no-create' ('-c') or '--no-dereference' ('-h') was in effect.
A FILE argument string of '-' is handled specially and causes 'touch'
to change the times of the file associated with standard output.
By default, 'touch' sets file timestamps to the current time.
Because 'touch' acts on its operands left to right, the resulting
timestamps of earlier and later operands may disagree. Also, the
determination of what time is "current" depends on the platform.
Platforms with network file systems often use different clocks for the
operating system and for file systems; because 'touch' typically uses
file systems' clocks by default, clock skew can cause the resulting file
timestamps to appear to be in a program's "future" or "past".
The 'touch' command sets the file's timestamp to the greatest
representable value that is not greater than the requested time. This
can differ from the requested time for several reasons. First, the
requested time may have a higher resolution than supported. Second, a
file system may use different resolutions for different types of times.
Third, file timestamps may use a different resolution than operating
system timestamps. Fourth, the operating system primitives used to
update timestamps may employ yet a different resolution. For example,
in theory a file system might use 10-microsecond resolution for access
time and 100-nanosecond resolution for modification time, and the
operating system might use nanosecond resolution for the current time
and microsecond resolution for the primitive that 'touch' uses to set a
file's timestamp to an arbitrary value.
When setting file timestamps to the current time, 'touch' can change
the timestamps for files that the user does not own but has write
permission for. Otherwise, the user must own the files. Some older
systems have a further restriction: the user must own the files unless
both the access and modification times are being set to the current
time.
Although 'touch' provides options for changing two of the times—the
times of last access and modification—of a file, there is actually a
standard third one as well: the inode change time. This is often
referred to as a file's 'ctime'. The inode change time represents the
time when the file's meta-information last changed. One common example
of this is when the permissions of a file change. Changing the
permissions doesn't access the file, so the atime doesn't change, nor
does it modify the file, so the mtime doesn't change. Yet, something
about the file itself has changed, and this must be noted somewhere.
This is the job of the ctime field. This is necessary, so that, for
example, a backup program can make a fresh copy of the file, including
the new permissions value. Another operation that modifies a file's
ctime without affecting the others is renaming. In any case, it is not
possible, in normal operations, for a user to change the ctime field to
a user-specified value. Some operating systems and file systems support
a fourth time: the birth time, when the file was first created; by
definition, this timestamp never changes.
Time stamps assume the time zone rules specified by the 'TZ'
environment variable, or by the system default rules if 'TZ' is not set.
*Note Specifying the Time Zone with 'TZ': (libc)TZ Variable. You can
avoid ambiguities during daylight saving transitions by using UTC time
stamps.
The program accepts the following options. Also see *note Common
options::.
'-a'
'--time=atime'
'--time=access'
'--time=use'
Change the access time only.
'-c'
'--no-create'
Do not warn about or create files that do not exist.
'-d'
'--date=TIME'
Use TIME instead of the current time. It can contain month names,
time zones, 'am' and 'pm', 'yesterday', etc. For example,
'--date="2004-02-27 14:19:13.489392193 +0530"' specifies the
instant of time that is 489,392,193 nanoseconds after February 27,
2004 at 2:19:13 PM in a time zone that is 5 hours and 30 minutes
east of UTC. *Note Date input formats::. File systems that do not
support high-resolution time stamps silently ignore any excess
precision here.
'-f'
Ignored; for compatibility with BSD versions of 'touch'.
'-h'
'--no-dereference'
Attempt to change the timestamps of a symbolic link, rather than
what the link refers to. When using this option, empty files are
not created, but option '-c' must also be used to avoid warning
about files that do not exist. Not all systems support changing
the timestamps of symlinks, since underlying system support for
this action was not required until POSIX 2008. Also, on some
systems, the mere act of examining a symbolic link changes the
access time, such that only changes to the modification time will
persist long enough to be observable. When coupled with option
'-r', a reference timestamp is taken from a symbolic link rather
than the file it refers to.
'-m'
'--time=mtime'
'--time=modify'
Change the modification time only.
'-r FILE'
'--reference=FILE'
Use the times of the reference FILE instead of the current time.
If this option is combined with the '--date=TIME' ('-d TIME')
option, the reference FILE's time is the origin for any relative
TIMEs given, but is otherwise ignored. For example, '-r foo -d '-5
seconds'' specifies a time stamp equal to five seconds before the
corresponding time stamp for 'foo'. If FILE is a symbolic link,
the reference timestamp is taken from the target of the symlink,
unless '-h' was also in effect.
'-t [[CC]YY]MMDDHHMM[.SS]'
Use the argument (optional four-digit or two-digit years, months,
days, hours, minutes, optional seconds) instead of the current
time. If the year is specified with only two digits, then CC is 20
for years in the range 0 ... 68, and 19 for years in 69 ... 99. If no
digits of the year are specified, the argument is interpreted as a
date in the current year. On the atypical systems that support
leap seconds, SS may be '60'.
On older systems, 'touch' supports an obsolete syntax, as follows.
If no timestamp is given with any of the '-d', '-r', or '-t' options,
and if there are two or more FILEs and the first FILE is of the form
'MMDDHHMM[YY]' and this would be a valid argument to the '-t' option (if
the YY, if any, were moved to the front), and if the represented year is
in the range 1969–1999, that argument is interpreted as the time for the
other files instead of as a file name. This obsolete behavior can be
enabled or disabled with the '_POSIX2_VERSION' environment variable
(*note Standards conformance::), but portable scripts should avoid
commands whose behavior depends on this variable. For example, use
'touch ./12312359 main.c' or 'touch -t 12312359 main.c' rather than the
ambiguous 'touch 12312359 main.c'.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'tr': Translate, squeeze, and/or delete characters
Synopsis:
tr [OPTION]... SET1 [SET2]
'tr' copies standard input to standard output, performing one of the
following operations:
• translate, and optionally squeeze repeated characters in the
result,
• squeeze repeated characters,
• delete characters,
• delete characters, then squeeze repeated characters from the
result.
The SET1 and (if given) SET2 arguments define ordered sets of
characters, referred to below as SET1 and SET2. These sets are the
characters of the input that 'tr' operates on. The '--complement'
('-c', '-C') option replaces SET1 with its complement (all of the
characters that are not in SET1).
Currently 'tr' fully supports only single-byte characters.
Eventually it will support multibyte characters; when it does, the '-C'
option will cause it to complement the set of characters, whereas '-c'
will cause it to complement the set of values. This distinction will
matter only when some values are not characters, and this is possible
only in locales using multibyte encodings when the input contains
encoding errors.
The program accepts the '--help' and '--version' options. *Note
Common options::. Options must precede operands.
An exit status of zero indicates success, and a nonzero value
indicates failure.
* Menu:
* Character sets:: Specifying sets of characters.
* Translating:: Changing one set of characters to another.
* Squeezing:: Squeezing repeats and deleting.
Specifying sets of characters
-----------------------------
The format of the SET1 and SET2 arguments resembles the format of
regular expressions; however, they are not regular expressions, only
lists of characters. Most characters simply represent themselves in
these strings, but the strings can contain the shorthands listed below,
for convenience. Some of them can be used only in SET1 or SET2, as
noted below.
Backslash escapes
The following backslash escape sequences are recognized:
'\a'
Control-G.
'\b'
Control-H.
'\f'
Control-L.
'\n'
Control-J.
'\r'
Control-M.
'\t'
Control-I.
'\v'
Control-K.
'\OOO'
The 8-bit character with the value given by OOO, which is 1 to
3 octal digits. Note that '\400' is interpreted as the
two-byte sequence, '\040' '0'.
'\\'
A backslash.
While a backslash followed by a character not listed above is
interpreted as that character, the backslash also effectively
removes any special significance, so it is useful to escape '[',
']', '*', and '-'.
Ranges
The notation 'M-N' expands to all of the characters from M through
N, in ascending order. M should collate before N; if it doesn't,
an error results. As an example, '0-9' is the same as
'0123456789'.
GNU 'tr' does not support the System V syntax that uses square
brackets to enclose ranges. Translations specified in that format
sometimes work as expected, since the brackets are often
transliterated to themselves. However, they should be avoided
because they sometimes behave unexpectedly. For example, 'tr -d
'[0-9]'' deletes brackets as well as digits.
Many historically common and even accepted uses of ranges are not
portable. For example, on EBCDIC hosts using the 'A-Z' range will
not do what most would expect because 'A' through 'Z' are not
contiguous as they are in ASCII. If you can rely on a POSIX
compliant version of 'tr', then the best way to work around this is
to use character classes (see below). Otherwise, it is most
portable (and most ugly) to enumerate the members of the ranges.
Repeated characters
The notation '[C*N]' in SET2 expands to N copies of character C.
Thus, '[y*6]' is the same as 'yyyyyy'. The notation '[C*]' in
STRING2 expands to as many copies of C as are needed to make SET2
as long as SET1. If N begins with '0', it is interpreted in octal,
otherwise in decimal.
Character classes
The notation '[:CLASS:]' expands to all of the characters in the
(predefined) class CLASS. The characters expand in no particular
order, except for the 'upper' and 'lower' classes, which expand in
ascending order. When the '--delete' ('-d') and
'--squeeze-repeats' ('-s') options are both given, any character
class can be used in SET2. Otherwise, only the character classes
'lower' and 'upper' are accepted in SET2, and then only if the
corresponding character class ('upper' and 'lower', respectively)
is specified in the same relative position in SET1. Doing this
specifies case conversion. The class names are given below; an
error results when an invalid class name is given.
'alnum'
Letters and digits.
'alpha'
Letters.
'blank'
Horizontal whitespace.
'cntrl'
Control characters.
'digit'
Digits.
'graph'
Printable characters, not including space.
'lower'
Lowercase letters.
'print'
Printable characters, including space.
'punct'
Punctuation characters.
'space'
Horizontal or vertical whitespace.
'upper'
Uppercase letters.
'xdigit'
Hexadecimal digits.
Equivalence classes
The syntax '[=C=]' expands to all of the characters that are
equivalent to C, in no particular order. Equivalence classes are a
relatively recent invention intended to support non-English
alphabets. But there seems to be no standard way to define them or
determine their contents. Therefore, they are not fully
implemented in GNU 'tr'; each character's equivalence class
consists only of that character, which is of no particular use.
Translating
-----------
'tr' performs translation when SET1 and SET2 are both given and the
'--delete' ('-d') option is not given. 'tr' translates each character
of its input that is in SET1 to the corresponding character in SET2.
Characters not in SET1 are passed through unchanged. When a character
appears more than once in SET1 and the corresponding characters in SET2
are not all the same, only the final one is used. For example, these
two commands are equivalent:
tr aaa xyz
tr a z
A common use of 'tr' is to convert lowercase characters to uppercase.
This can be done in many ways. Here are three of them:
tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
tr a-z A-Z
tr '[:lower:]' '[:upper:]'
But note that using ranges like 'a-z' above is not portable.
When 'tr' is performing translation, SET1 and SET2 typically have the
same length. If SET1 is shorter than SET2, the extra characters at the
end of SET2 are ignored.
On the other hand, making SET1 longer than SET2 is not portable;
POSIX says that the result is undefined. In this situation, BSD 'tr'
pads SET2 to the length of SET1 by repeating the last character of SET2
as many times as necessary. System V 'tr' truncates SET1 to the length
of SET2.
By default, GNU 'tr' handles this case like BSD 'tr'. When the
'--truncate-set1' ('-t') option is given, GNU 'tr' handles this case
like the System V 'tr' instead. This option is ignored for operations
other than translation.
Acting like System V 'tr' in this case breaks the relatively common
BSD idiom:
tr -cs A-Za-z0-9 '\012'
because it converts only zero bytes (the first element in the complement
of SET1), rather than all non-alphanumerics, to newlines.
By the way, the above idiom is not portable because it uses ranges, and
it assumes that the octal code for newline is 012. Assuming a POSIX
compliant 'tr', here is a better way to write it:
tr -cs '[:alnum:]' '[\n*]'
Squeezing repeats and deleting
------------------------------
When given just the '--delete' ('-d') option, 'tr' removes any input
characters that are in SET1.
When given just the '--squeeze-repeats' ('-s') option, 'tr' replaces
each input sequence of a repeated character that is in SET1 with a
single occurrence of that character.
When given both '--delete' and '--squeeze-repeats', 'tr' first
performs any deletions using SET1, then squeezes repeats from any
remaining characters using SET2.
The '--squeeze-repeats' option may also be used when translating, in
which case 'tr' first performs translation, then squeezes repeats from
any remaining characters using SET2.
Here are some examples to illustrate various combinations of options:
• Remove all zero bytes:
tr -d '\0'
• Put all words on lines by themselves. This converts all
non-alphanumeric characters to newlines, then squeezes each string
of repeated newlines into a single newline:
tr -cs '[:alnum:]' '[\n*]'
• Convert each sequence of repeated newlines to a single newline:
tr -s '\n'
• Find doubled occurrences of words in a document. For example,
people often write "the the" with the repeated words separated by a
newline. The Bourne shell script below works first by converting
each sequence of punctuation and blank characters to a single
newline. That puts each "word" on a line by itself. Next it maps
all uppercase characters to lower case, and finally it runs 'uniq'
with the '-d' option to print out only the words that were
repeated.
#!/bin/sh
cat -- "$@" \
| tr -s '[:punct:][:blank:]' '[\n*]' \
| tr '[:upper:]' '[:lower:]' \
| uniq -d
• Deleting a small set of characters is usually straightforward. For
example, to remove all 'a's, 'x's, and 'M's you would do this:
tr -d axM
However, when '-' is one of those characters, it can be tricky
because '-' has special meanings. Performing the same task as
above but also removing all '-' characters, we might try 'tr -d
-axM', but that would fail because 'tr' would try to interpret '-a'
as a command-line option. Alternatively, we could try putting the
hyphen inside the string, 'tr -d a-xM', but that wouldn't work
either because it would make 'tr' interpret 'a-x' as the range of
characters 'a'...'x' rather than the three. One way to solve the
problem is to put the hyphen at the end of the list of characters:
tr -d axM-
Or you can use '--' to terminate option processing:
tr -d -- -axM
More generally, use the character class notation '[=c=]' with '-'
(or any other character) in place of the 'c':
tr -d '[=-=]axM'
Note how single quotes are used in the above example to protect the
square brackets from interpretation by a shell.
(builtin command)
trap: trap [-lp] [[arg] signal_spec ...]
Trap signals and other events.
Defines and activates handlers to be run when the shell receives signals
or other conditions.
ARG is a command to be read and executed when the shell receives the
signal(s) SIGNAL_SPEC. If ARG is absent (and a single SIGNAL_SPEC
is supplied) or '-', each specified signal is reset to its original
value. If ARG is the null string each SIGNAL_SPEC is ignored by the
shell and by the commands it invokes.
If a SIGNAL_SPEC is EXIT (0) ARG is executed on exit from the shell. If
a SIGNAL_SPEC is DEBUG, ARG is executed before every simple command. If
a SIGNAL_SPEC is RETURN, ARG is executed each time a shell function or a
script run by the . or source builtins finishes executing. A SIGNAL_SPEC
of ERR means to execute ARG each time a command's failure would cause the
shell to exit when the -e option is enabled.
If no arguments are supplied, trap prints the list of commands associated
with each signal.
Options:
-l print a list of signal names and their corresponding numbers
-p display the trap commands associated with each SIGNAL_SPEC
Each SIGNAL_SPEC is either a signal name in <signal.h> or a signal number.
Signal names are case insensitive and the SIG prefix is optional. A
signal may be sent to the shell with "kill -signal $$".
Exit Status:
Returns success unless a SIGSPEC is invalid or an invalid option is given.
(coreutils)
'true': Do nothing, successfully
'true' does nothing except return an exit status of 0, meaning
"success". It can be used as a place holder in shell scripts where a
successful command is needed, although the shell built-in command ':'
(colon) may do the same thing faster. In most modern shells, 'true' is
a built-in command, so when you use 'true' in a script, you're probably
using the built-in command, not the one documented here.
'true' honors the '--help' and '--version' options.
Note, however, that it is possible to cause 'true' to exit with
nonzero status: with the '--help' or '--version' option, and with
standard output already closed or redirected to a file that evokes an
I/O error. For example, using a Bourne-compatible shell:
$ ./true --version >&-
./true: write error: Bad file number
$ ./true --version > /dev/full
./true: write error: No space left on device
This version of 'true' is implemented as a C program, and is thus
more secure and faster than a shell script implementation, and may
safely be used as a dummy shell for the purpose of disabling accounts.
(coreutils)
'true': Do nothing, successfully
'true' does nothing except return an exit status of 0, meaning
"success". It can be used as a place holder in shell scripts where a
successful command is needed, although the shell built-in command ':'
(colon) may do the same thing faster. In most modern shells, 'true' is
a built-in command, so when you use 'true' in a script, you're probably
using the built-in command, not the one documented here.
'true' honors the '--help' and '--version' options.
Note, however, that it is possible to cause 'true' to exit with
nonzero status: with the '--help' or '--version' option, and with
standard output already closed or redirected to a file that evokes an
I/O error. For example, using a Bourne-compatible shell:
$ ./true --version >&-
./true: write error: Bad file number
$ ./true --version > /dev/full
./true: write error: No space left on device
This version of 'true' is implemented as a C program, and is thus
more secure and faster than a shell script implementation, and may
safely be used as a dummy shell for the purpose of disabling accounts.
(coreutils)
'truncate': Shrink or extend the size of a file
'truncate' shrinks or extends the size of each FILE to the specified
size. Synopsis:
truncate OPTION... FILE...
Any FILE that does not exist is created.
If a FILE is larger than the specified size, the extra data is lost.
If a FILE is shorter, it is extended and the extended part (or hole)
reads as zero bytes.
The program accepts the following options. Also see *note Common
options::.
'-c'
'--no-create'
Do not create files that do not exist.
'-o'
'--io-blocks'
Treat SIZE as number of I/O blocks of the FILE rather than bytes.
'-r RFILE'
'--reference=RFILE'
Base the size of each FILE on the size of RFILE.
'-s SIZE'
'--size=SIZE'
Set or adjust the size of each FILE according to SIZE. SIZE is in
bytes unless '--io-blocks' is specified. SIZE may be, or may be an
integer optionally followed by, one of the following multiplicative
suffixes:
'KB' => 1000 (KiloBytes)
'K' => 1024 (KibiBytes)
'MB' => 1000*1000 (MegaBytes)
'M' => 1024*1024 (MebiBytes)
'GB' => 1000*1000*1000 (GigaBytes)
'G' => 1024*1024*1024 (GibiBytes)
and so on for 'T', 'P', 'E', 'Z', and 'Y'.
SIZE may also be prefixed by one of the following to adjust the
size of each FILE based on their current size:
'+' => extend by
'-' => reduce by
'<' => at most
'>' => at least
'/' => round down to multiple of
'%' => round up to multiple of
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'tsort': Topological sort
'tsort' performs a topological sort on the given FILE, or standard input
if no input file is given or for a FILE of '-'. For more details and
some history, see *note tsort background::. Synopsis:
tsort [OPTION] [FILE]
'tsort' reads its input as pairs of strings, separated by blanks,
indicating a partial ordering. The output is a total ordering that
corresponds to the given partial ordering.
For example
tsort <<EOF
a b c
d
e f
b c d e
EOF
will produce the output
a
b
c
d
e
f
Consider a more realistic example. You have a large set of functions
all in one file, and they may all be declared static except one.
Currently that one (say 'main') is the first function defined in the
file, and the ones it calls directly follow it, followed by those they
call, etc. Let's say that you are determined to take advantage of
prototypes, so you have to choose between declaring all of those
functions (which means duplicating a lot of information from the
definitions) and rearranging the functions so that as many as possible
are defined before they are used. One way to automate the latter
process is to get a list for each function of the functions it calls
directly. Many programs can generate such lists. They describe a call
graph. Consider the following list, in which a given line indicates
that the function on the left calls the one on the right directly.
main parse_options
main tail_file
main tail_forever
tail_file pretty_name
tail_file write_header
tail_file tail
tail_forever recheck
tail_forever pretty_name
tail_forever write_header
tail_forever dump_remainder
tail tail_lines
tail tail_bytes
tail_lines start_lines
tail_lines dump_remainder
tail_lines file_lines
tail_lines pipe_lines
tail_bytes xlseek
tail_bytes start_bytes
tail_bytes dump_remainder
tail_bytes pipe_bytes
file_lines dump_remainder
recheck pretty_name
then you can use 'tsort' to produce an ordering of those functions
that satisfies your requirement.
example$ tsort call-graph | tac
dump_remainder
start_lines
file_lines
pipe_lines
xlseek
start_bytes
pipe_bytes
tail_lines
tail_bytes
pretty_name
write_header
tail
recheck
parse_options
tail_file
tail_forever
main
'tsort' detects any cycles in the input and writes the first cycle
encountered to standard error.
Note that for a given partial ordering, generally there is no unique
total ordering. In the context of the call graph above, the function
'parse_options' may be placed anywhere in the list as long as it
precedes 'main'.
The only options are '--help' and '--version'. *Note Common
options::.
An exit status of zero indicates success, and a nonzero value
indicates failure.
* Menu:
* tsort background:: Where tsort came from.
'tsort': Background
-------------------
'tsort' exists because very early versions of the Unix linker processed
an archive file exactly once, and in order. As 'ld' read each object in
the archive, it decided whether it was needed in the program based on
whether it defined any symbols which were undefined at that point in the
link.
This meant that dependencies within the archive had to be handled
specially. For example, 'scanf' probably calls 'read'. That means that
in a single pass through an archive, it was important for 'scanf.o' to
appear before read.o, because otherwise a program which calls 'scanf'
but not 'read' might end up with an unexpected unresolved reference to
'read'.
The way to address this problem was to first generate a set of
dependencies of one object file on another. This was done by a shell
script called 'lorder'. The GNU tools don't provide a version of
lorder, as far as I know, but you can still find it in BSD
distributions.
Then you ran 'tsort' over the 'lorder' output, and you used the
resulting sort to define the order in which you added objects to the
archive.
This whole procedure has been obsolete since about 1980, because Unix
archives now contain a symbol table (traditionally built by 'ranlib',
now generally built by 'ar' itself), and the Unix linker uses the symbol
table to effectively make multiple passes over an archive file.
Anyhow, that's where tsort came from. To solve an old problem with
the way the linker handled archive files, which has since been solved in
different ways.
(coreutils)
'tty': Print file name of terminal on standard input
'tty' prints the file name of the terminal connected to its standard
input. It prints 'not a tty' if standard input is not a terminal.
Synopsis:
tty [OPTION]...
The program accepts the following option. Also see *note Common
options::.
'-s'
'--silent'
'--quiet'
Print nothing; only return an exit status.
Exit status:
0 if standard input is a terminal
1 if standard input is not a terminal
2 if given incorrect arguments
3 if a write error occurs
(builtin command)
type: type [-afptP] name [name ...]
Display information about command type.
For each NAME, indicate how it would be interpreted if used as a
command name.
Options:
-a display all locations containing an executable named NAME;
includes aliases, builtins, and functions, if and only if
the '-p' option is not also used
-f suppress shell function lookup
-P force a PATH search for each NAME, even if it is an alias,
builtin, or function, and returns the name of the disk file
that would be executed
-p returns either the name of the disk file that would be executed,
or nothing if 'type -t NAME' would not return 'file'.
-t output a single word which is one of 'alias', 'keyword',
'function', 'builtin', 'file' or '', if NAME is an alias, shell
reserved word, shell function, shell builtin, disk file, or not
found, respectively
Arguments:
NAME Command name to be interpreted.
Exit Status:
Returns success if all of the NAMEs are found; fails if any are not found.
(builtin command)
typeset: typeset [-aAfFgilrtux] [-p] name[=value] ...
Set variable values and attributes.
Obsolete. See 'help declare'.
(builtin command)
ulimit: ulimit [-SHabcdefilmnpqrstuvxT] [limit]
Modify shell resource limits.
Provides control over the resources available to the shell and processes
it creates, on systems that allow such control.
Options:
-S use the 'soft' resource limit
-H use the 'hard' resource limit
-a all current limits are reported
-b the socket buffer size
-c the maximum size of core files created
-d the maximum size of a process's data segment
-e the maximum scheduling priority ('nice')
-f the maximum size of files written by the shell and its children
-i the maximum number of pending signals
-l the maximum size a process may lock into memory
-m the maximum resident set size
-n the maximum number of open file descriptors
-p the pipe buffer size
-q the maximum number of bytes in POSIX message queues
-r the maximum real-time scheduling priority
-s the maximum stack size
-t the maximum amount of cpu time in seconds
-u the maximum number of user processes
-v the size of virtual memory
-x the maximum number of file locks
-T the maximum number of threads
Not all options are available on all platforms.
If LIMIT is given, it is the new value of the specified resource; the
special LIMIT values 'soft', 'hard', and 'unlimited' stand for the
current soft limit, the current hard limit, and no limit, respectively.
Otherwise, the current value of the specified resource is printed. If
no option is given, then -f is assumed.
Values are in 1024-byte increments, except for -t, which is in seconds,
-p, which is in increments of 512 bytes, and -u, which is an unscaled
number of processes.
Exit Status:
Returns success unless an invalid option is supplied or an error occurs.
(builtin command)
umask: umask [-p] [-S] [mode]
Display or set file mode mask.
Sets the user file-creation mask to MODE. If MODE is omitted, prints
the current value of the mask.
If MODE begins with a digit, it is interpreted as an octal number;
otherwise it is a symbolic mode string like that accepted by chmod(1).
Options:
-p if MODE is omitted, output in a form that may be reused as input
-S makes the output symbolic; otherwise an octal number is output
Exit Status:
Returns success unless MODE is invalid or an invalid option is given.
(builtin command)
unalias: unalias [-a] name [name ...]
Remove each NAME from the list of defined aliases.
Options:
-a remove all alias definitions.
Return success unless a NAME is not an existing alias.
(coreutils)
'uname': Print system information
'uname' prints information about the machine and operating system it is
run on. If no options are given, 'uname' acts as if the '-s' option
were given. Synopsis:
uname [OPTION]...
If multiple options or '-a' are given, the selected information is
printed in this order:
KERNEL-NAME NODENAME KERNEL-RELEASE KERNEL-VERSION
MACHINE PROCESSOR HARDWARE-PLATFORM OPERATING-SYSTEM
The information may contain internal spaces, so such output cannot be
parsed reliably. In the following example, RELEASE is
'2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001':
uname -a
⇒ Linux dumdum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
The program accepts the following options. Also see *note Common
options::.
'-a'
'--all'
Print all of the below information, except omit the processor type
and the hardware platform name if they are unknown.
'-i'
'--hardware-platform'
Print the hardware platform name (sometimes called the hardware
implementation). Print 'unknown' if the kernel does not make this
information easily available, as is the case with Linux kernels.
'-m'
'--machine'
Print the machine hardware name (sometimes called the hardware
class or hardware type).
'-n'
'--nodename'
Print the network node hostname.
'-p'
'--processor'
Print the processor type (sometimes called the instruction set
architecture or ISA). Print 'unknown' if the kernel does not make
this information easily available, as is the case with Linux
kernels.
'-o'
'--operating-system'
Print the name of the operating system.
'-r'
'--kernel-release'
Print the kernel release.
'-s'
'--kernel-name'
Print the kernel name. POSIX 1003.1-2001 (*note Standards
conformance::) calls this "the implementation of the operating
system", because the POSIX specification itself has no notion of
"kernel". The kernel name might be the same as the operating
system name printed by the '-o' or '--operating-system' option, but
it might differ. Some operating systems (e.g., FreeBSD, HP-UX)
have the same name as their underlying kernels; others (e.g.,
GNU/Linux, Solaris) do not.
'-v'
'--kernel-version'
Print the kernel version.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'unexpand': Convert spaces to tabs
'unexpand' writes the contents of each given FILE, or standard input if
none are given or for a FILE of '-', to standard output, converting
blanks at the beginning of each line into as many tab characters as
needed. In the default POSIX locale, a "blank" is a space or a tab;
other locales may specify additional blank characters. Synopsis:
unexpand [OPTION]... [FILE]...
By default, 'unexpand' converts only initial blanks (those that
precede all non-blank characters) on each line. It preserves backspace
characters in the output; they decrement the column count for tab
calculations. By default, tabs are set at every 8th column.
The program accepts the following options. Also see *note Common
options::.
'-t TAB1[,TAB2]...'
'--tabs=TAB1[,TAB2]...'
If only one tab stop is given, set the tabs TAB1 columns apart
instead of the default 8. Otherwise, set the tabs at columns TAB1,
TAB2, ... (numbered from 0), and leave blanks beyond the tab stops
given unchanged. Tab stops can be separated by blanks as well as
by commas. This option implies the '-a' option.
For compatibility, GNU 'unexpand' supports the obsolete option
syntax, '-TAB1[,TAB2]...', where tab stops must be separated by
commas. (Unlike '-t', this obsolete option does not imply '-a'.)
New scripts should use '--first-only -t TAB1[,TAB2]...' instead.
'-a'
'--all'
Also convert all sequences of two or more blanks just before a tab
stop, even if they occur after non-blank characters in a line.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'uniq': Uniquify files
'uniq' writes the unique lines in the given 'input', or standard input
if nothing is given or for an INPUT name of '-'. Synopsis:
uniq [OPTION]... [INPUT [OUTPUT]]
By default, 'uniq' prints its input lines, except that it discards
all but the first of adjacent repeated lines, so that no output lines
are repeated. Optionally, it can instead discard lines that are not
repeated, or all repeated lines.
The input need not be sorted, but repeated input lines are detected
only if they are adjacent. If you want to discard non-adjacent
duplicate lines, perhaps you want to use 'sort -u'. *Note sort
invocation::.
Comparisons honor the rules specified by the 'LC_COLLATE' locale
category.
If no OUTPUT file is specified, 'uniq' writes to standard output.
The program accepts the following options. Also see *note Common
options::.
'-f N'
'--skip-fields=N'
Skip N fields on each line before checking for uniqueness. Use a
null string for comparison if a line has fewer than N fields.
Fields are sequences of non-space non-tab characters that are
separated from each other by at least one space or tab.
For compatibility 'uniq' supports an obsolete option syntax '-N'.
New scripts should use '-f N' instead.
'-s N'
'--skip-chars=N'
Skip N characters before checking for uniqueness. Use a null
string for comparison if a line has fewer than N characters. If
you use both the field and character skipping options, fields are
skipped over first.
On older systems, 'uniq' supports an obsolete option syntax '+N'.
This obsolete behavior can be enabled or disabled with the
'_POSIX2_VERSION' environment variable (*note Standards
conformance::), but portable scripts should avoid commands whose
behavior depends on this variable. For example, use 'uniq ./+10'
or 'uniq -s 10' rather than the ambiguous 'uniq +10'.
'-c'
'--count'
Print the number of times each line occurred along with the line.
'-i'
'--ignore-case'
Ignore differences in case when comparing lines.
'-d'
'--repeated'
Discard lines that are not repeated. When used by itself, this
option causes 'uniq' to print the first copy of each repeated line,
and nothing else.
'-D'
'--all-repeated[=DELIMIT-METHOD]'
Do not discard the second and subsequent repeated input lines, but
discard lines that are not repeated. This option is useful mainly
in conjunction with other options e.g., to ignore case or to
compare only selected fields. The optional DELIMIT-METHOD
specifies how to delimit groups of repeated lines, and must be one
of the following:
'none'
Do not delimit groups of repeated lines. This is equivalent
to '--all-repeated' ('-D').
'prepend'
Output a newline before each group of repeated lines. With
'--zero-terminated' ('-z'), use a zero byte (ASCII NUL)
instead of a newline as the delimiter.
'separate'
Separate groups of repeated lines with a single newline. This
is the same as using 'prepend', except that no delimiter is
inserted before the first group, and hence may be better
suited for output direct to users. With '--zero-terminated'
('-z'), use a zero byte (ASCII NUL) instead of a newline as
the delimiter.
Note that when groups are delimited and the input stream contains
two or more consecutive blank lines, then the output is ambiguous.
To avoid that, filter the input through 'tr -s '\n'' to replace
each sequence of consecutive newlines with a single newline.
This is a GNU extension.
'--group[=DELIMIT-METHOD]'
Output all lines, and delimit each unique group. With
'--zero-terminated' ('-z'), use a zero byte (ASCII NUL) instead of
a newline as the delimiter. The optional DELIMIT-METHOD specifies
how to delimit groups, and must be one of the following:
'separate'
Separate unique groups with a single delimiter. This is the
default delimiting method if none is specified, and better
suited for output direct to users.
'prepend'
Output a delimiter before each group of unique items.
'append'
Output a delimiter after each group of unique items.
'both'
Output a delimiter around each group of unique items.
Note that when groups are delimited and the input stream contains
two or more consecutive blank lines, then the output is ambiguous.
To avoid that, filter the input through 'tr -s '\n'' to replace
each sequence of consecutive newlines with a single newline.
This is a GNU extension.
'-u'
'--unique'
Discard the last line that would be output for a repeated input
group. When used by itself, this option causes 'uniq' to print
unique lines, and nothing else.
'-w N'
'--check-chars=N'
Compare at most N characters on each line (after skipping any
specified fields and characters). By default the entire rest of
the lines are compared.
'-z'
'--zero-terminated'
Delimit items with a zero byte rather than a newline (ASCII LF).
I.e., treat input as items separated by ASCII NUL and terminate
output items with ASCII NUL. This option can be useful in
conjunction with 'perl -0' or 'find -print0' and 'xargs -0' which
do the same in order to reliably handle arbitrary file names (even
those containing blanks or other special characters).
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'unlink': Remove files via the unlink syscall
'unlink' deletes a single specified file name. It is a minimalist
interface to the system-provided 'unlink' function. *Note
(libc)Deleting Files::. Synopsis: It avoids the bells and whistles of
the more commonly-used 'rm' command (*note rm invocation::).
unlink FILENAME
On some systems 'unlink' can be used to delete the name of a
directory. On others, it can be used that way only by a privileged
user. In the GNU system 'unlink' can never delete the name of a
directory.
The 'unlink' command honors the '--help' and '--version' options. To
remove a file whose name begins with '-', prefix the name with './',
e.g., 'unlink ./--help'.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(builtin command)
unset: unset [-f] [-v] [-n] [name ...]
Unset values and attributes of shell variables and functions.
For each NAME, remove the corresponding variable or function.
Options:
-f treat each NAME as a shell function
-v treat each NAME as a shell variable
-n treat each NAME as a name reference and unset the variable itself
rather than the variable it references
Without options, unset first tries to unset a variable, and if that fails,
tries to unset a function.
Some variables cannot be unset; also see 'readonly'.
Exit Status:
Returns success unless an invalid option is given or a NAME is read-only.
(reserved word)
until: until COMMANDS; do COMMANDS; done
Execute commands as long as a test does not succeed.
Expand and execute COMMANDS as long as the final command in the
'until' COMMANDS has an exit status which is not zero.
Exit Status:
Returns the status of the last command executed.
(coreutils)
'uptime': Print system uptime and load
'uptime' prints the current time, the system's uptime, the number of
logged-in users and the current load average.
If an argument is specified, it is used as the file to be read to
discover how many users are logged in. If no argument is specified, a
system default is used ('uptime --help' indicates the default setting).
The only options are '--help' and '--version'. *Note Common
options::.
For example, here's what it prints right now on one system I use:
$ uptime
14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
The precise method of calculation of load average varies somewhat
between systems. Some systems calculate it as the average number of
runnable processes over the last 1, 5 and 15 minutes, but some systems
also include processes in the uninterruptible sleep state (that is,
those processes which are waiting for disk I/O). The Linux kernel
includes uninterruptible processes.
(coreutils)
'users': Print login names of users currently logged in
'users' prints on a single line a blank-separated list of user names of
users currently logged in to the current host. Each user name
corresponds to a login session, so if a user has more than one login
session, that user's name will appear the same number of times in the
output. Synopsis:
users [FILE]
With no FILE argument, 'users' extracts its information from a
system-maintained file (often '/var/run/utmp' or '/etc/utmp'). If a
file argument is given, 'users' uses that file instead. A common choice
is '/var/log/wtmp'.
The only options are '--help' and '--version'. *Note Common
options::.
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'vdir': Verbosely list directory contents 'vdir' is equivalent to 'ls -l -b'; that is, by default files are listed in long format and special characters are represented by backslash escape sequences.
(builtin command)
wait: wait [-n] [id ...]
Wait for job completion and return exit status.
Waits for each process identified by an ID, which may be a process ID or a
job specification, and reports its termination status. If ID is not
given, waits for all currently active child processes, and the return
status is zero. If ID is a a job specification, waits for all processes
in that job's pipeline.
If the -n option is supplied, waits for the next job to terminate and
returns its exit status.
Exit Status:
Returns the status of the last ID; fails if ID is invalid or an invalid
option is given.
(coreutils)
'wc': Print newline, word, and byte counts
'wc' counts the number of bytes, characters, whitespace-separated words,
and newlines in each given FILE, or standard input if none are given or
for a FILE of '-'. Synopsis:
wc [OPTION]... [FILE]...
'wc' prints one line of counts for each file, and if the file was
given as an argument, it prints the file name following the counts. If
more than one FILE is given, 'wc' prints a final line containing the
cumulative counts, with the file name 'total'. The counts are printed
in this order: newlines, words, characters, bytes, maximum line length.
Each count is printed right-justified in a field with at least one space
between fields so that the numbers and file names normally line up
nicely in columns. The width of the count fields varies depending on
the inputs, so you should not depend on a particular field width.
However, as a GNU extension, if only one count is printed, it is
guaranteed to be printed without leading spaces.
By default, 'wc' prints three counts: the newline, words, and byte
counts. Options can specify that only certain counts be printed.
Options do not undo others previously given, so
wc --bytes --words
prints both the byte counts and the word counts.
With the '--max-line-length' option, 'wc' prints the length of the
longest line per file, and if there is more than one file it prints the
maximum (not the sum) of those lengths. The line lengths here are
measured in screen columns, according to the current locale and assuming
tab positions in every 8th column.
The program accepts the following options. Also see *note Common
options::.
'-c'
'--bytes'
Print only the byte counts.
'-m'
'--chars'
Print only the character counts.
'-w'
'--words'
Print only the word counts.
'-l'
'--lines'
Print only the newline counts.
'-L'
'--max-line-length'
Print only the maximum line lengths.
'--files0-from=FILE'
Disallow processing files named on the command line, and instead
process those named in file FILE; each name being terminated by a
zero byte (ASCII NUL). This is useful when the list of file names
is so long that it may exceed a command line length limitation. In
such cases, running 'wc' via 'xargs' is undesirable because it
splits the list into pieces and makes 'wc' print a total for each
sublist rather than for the entire list. One way to produce a list
of ASCII NUL terminated file names is with GNU 'find', using its
'-print0' predicate. If FILE is '-' then the ASCII NUL terminated
file names are read from standard input.
For example, to find the length of the longest line in any '.c' or
'.h' file in the current hierarchy, do this:
find . -name '*.[ch]' -print0 |
wc -L --files0-from=- | tail -n1
An exit status of zero indicates success, and a nonzero value
indicates failure.
(reserved word)
while: while COMMANDS; do COMMANDS; done
Execute commands as long as a test succeeds.
Expand and execute COMMANDS as long as the final command in the
'while' COMMANDS has an exit status of zero.
Exit Status:
Returns the status of the last command executed.
(coreutils)
'who': Print who is currently logged in
'who' prints information about users who are currently logged on.
Synopsis:
who [OPTION] [FILE] [am i]
If given no non-option arguments, 'who' prints the following
information for each user currently logged on: login name, terminal
line, login time, and remote hostname or X display.
If given one non-option argument, 'who' uses that instead of a
default system-maintained file (often '/var/run/utmp' or '/etc/utmp') as
the name of the file containing the record of users logged on.
'/var/log/wtmp' is commonly given as an argument to 'who' to look at who
has previously logged on.
If given two non-option arguments, 'who' prints only the entry for
the user running it (determined from its standard input), preceded by
the hostname. Traditionally, the two arguments given are 'am i', as in
'who am i'.
Time stamps are listed according to the time zone rules specified by
the 'TZ' environment variable, or by the system default rules if 'TZ' is
not set. *Note Specifying the Time Zone with 'TZ': (libc)TZ Variable.
The program accepts the following options. Also see *note Common
options::.
'-a'
'--all'
Same as '-b -d --login -p -r -t -T -u'.
'-b'
'--boot'
Print the date and time of last system boot.
'-d'
'--dead'
Print information corresponding to dead processes.
'-H'
'--heading'
Print a line of column headings.
'-l'
'--login'
List only the entries that correspond to processes via which the
system is waiting for a user to login. The user name is always
'LOGIN'.
'--lookup'
Attempt to canonicalize hostnames found in utmp through a DNS
lookup. This is not the default because it can cause significant
delays on systems with automatic dial-up internet access.
'-m'
Same as 'who am i'.
'-p'
'--process'
List active processes spawned by init.
'-q'
'--count'
Print only the login names and the number of users logged on.
Overrides all other options.
'-r'
'--runlevel'
Print the current (and maybe previous) run-level of the init
process.
'-s'
Ignored; for compatibility with other versions of 'who'.
'-t'
'--time'
Print last system clock change.
'-u'
After the login time, print the number of hours and minutes that
the user has been idle. '.' means the user was active in the last
minute. 'old' means the user has been idle for more than 24 hours.
'-w'
'-T'
'--mesg'
'--message'
'--writable'
After each login name print a character indicating the user's
message status:
'+' allowing 'write' messages
'-' disallowing 'write' messages
'?' cannot find terminal device
An exit status of zero indicates success, and a nonzero value
indicates failure.
(coreutils)
'whoami': Print effective user ID 'whoami' prints the user name associated with the current effective user ID. It is equivalent to the command 'id -un'. The only options are '--help' and '--version'. *Note Common options::. An exit status of zero indicates success, and a nonzero value indicates failure.
(coreutils)
'yes': Print a string until interrupted 'yes' prints the command line arguments, separated by spaces and followed by a newline, forever until it is killed. If no arguments are given, it prints 'y' followed by a newline forever until killed. Upon a write error, 'yes' exits with status '1'. The only options are a lone '--help' or '--version'. To output an argument that begins with '-', precede it with '--', e.g., 'yes -- --help'. *Note Common options::.
| Note: | Not all reserved words are listed here, only the ones for which help is available. |
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