IF

C:\>if /?

Performs conditional processing in batch programs.

IF [NOT] ERRORLEVEL number command
IF [NOT] string1==string2 command
IF [NOT] EXIST filename command

  NOT               Specifies that Windows XP should carry out  the command only if the condition is false.

  ERRORLEVEL number Specifies a true condition if the last program run returned an exit code equal to or greater than the number

                    specified.

  string1==string2  Specifies a true condition if the specified text strings  match.

  EXIST filename    Specifies a true condition if the specified filename exists.

  command           Specifies the command to carry out if the condition is  met.  Command can be followed by ELSE command which  will execute the command after the ELSE keyword if the specified condition is FALSE 

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:

    EQU - equal
    NEQ - not equal
    LSS - less than
    LEQ - less than or equal
    GTR - greater than
    GEQ - greater than or equal

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.  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.  After running a program, the following illustrates ERRORLEVEL use:

     goto answer%ERRORLEVEL%
    :answer0
    echo Program had return code 0
    :answer1
    echo Program had return code 1

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.

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