IF

Windows NT 4/2000/XP Syntax

Performs conditional processing in batch programs.

The ELSE clause must occur on the same line as the command after the IF.
For example:

    IF EXIST filename (
		del filename
	) ELSE (
		echo filename missing.
	)

The following would NOT work because the del command needs to be terminated by a newline:

    IF EXIST filename DEL filename ELSE ECHO filename missing

Nor would the following work, since the ELSE command must be on the same line as the end of the IF command:

    IF EXIST filename DEL filename
	ELSE ECHO filename missing

The following would work if you want it all on one line:

    IF EXIST filename (DEL filename) ELSE (ECHO filename missing)

If Command Extensions are enabled IF changes as follows:

    IF [/I] string1 compare-op string2 command
	IF CMDEXTVERSION number command
	IF DEFINED variable command

where compare-op may be one of:

and the /I switch, if specified, says to do case insensitive string compares. The /I switch can also be used on the string1==string2 form of IF. These comparisons are generic, in that if both string1 and string2 are both comprised of all numeric digits, then the strings are converted to numbers and a numeric comparison is performed.

The CMDEXTVERSION conditional works just like ERRORLEVEL, except it is comparing against an internal version number associated with the Command Extensions. The first version is 1 (NT 4), in Windows 2000 and XP CMDEXTVERSION is 2. It will be incremented by one when significant enhancements are added to the Command Extensions.
CMDEXTVERSION conditional is never true when Command Extensions are disabled.

The DEFINED conditional works just like EXISTS except it takes an environment variable name and returns true if the environment variable is defined.

%ERRORLEVEL% will expand into a string representation of the current value of ERRORLEVEL, provided that there is not already an environment variable with the name ERRORLEVEL, in which case you will get its value instead. Using this and the above numerical comparison operators, you can do the following (note: CHOICE is not part of Windows NT /Windows 2000's standard distribution):

    CHOICE
	GOTO answer%ERRORLEVEL%

	:answer0
	ECHO You typed Y for yes

	:answer1
	ECHO You typed N for no

you can also using the numerical comparisons above:

    IF %ERRORLEVEL% LEQ 1 goto okay

%CMDCMDLINE% will expand into the original command line passed to CMD.EXE prior to any processing by CMD.EXE, provided that there is not already an environment variable with the name CMDCMDLINE, in which case you will get its value instead.

%CMDEXTVERSION% will expand into a string representation of the current value of CMDEXTVERSION, provided that there is not already an environment variable with the name CMDEXTVERSION, in which case you will get its value instead.