if (执行批处理程序中的条件处理)

Windows Vista and later syntax

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

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 example below 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 example below work, because 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 example below 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, if both string1 and string2 are composed of all numeric digits, then they're converted to numbers and a numeric comparison is performed.

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

%ERRORLEVEL% expands into a string of the current value of ERRORLEVEL, provided there is not already an environment variable with the name ERRORLEVEL, in which case you get its value. After running a program, the example below illustrates ERRORLEVEL use:

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

You can also use the numerical comparisons below:

IF %ERRORLEVEL% LEQ 1 goto okay

%CMDCMDLINE% expands to the command line passed to CMD.EXE before any processing by CMD.EXE, provided there is not a CMDCMDLINE environment variable, in which case you get its value.

%CMDEXTVERSION% expands into a string of the value of CMDEXTVERSION, provided there is not already an environment variable with the name CMDEXTVERSION, in which case you get its value.

Windows XP and earlier syntax

Performs conditional processing in batch programs.

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