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

NOT

Specifies that Windows 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.