IF – Windows CMD Command

Conditionally perform a command.

File syntax
   IF [NOT] EXIST filename command

   IF [NOT] EXIST filename (command) ELSE (command)

String syntax
   IF [/I] [NOT] item1==item2 command 

   IF [/I] item1 compare-op item2 command

   IF [/I] item1 compare-op item2 (command) ELSE (command)

Error Check Syntax
   IF [NOT] DEFINED variable command

   IF [NOT] ERRORLEVEL number command 

   IF CMDEXTVERSION number command

key
   item        A text string or environment variable, for more complex
               comparisons, a variable can be modified using
               either Substring or Search syntax.

   command     The command to perform.

   filename    A file to test or a wildcard pattern.

   NOT         perform the command if the condition is false. 

   ==          perform the command if the two strings are equal. 

   /I          Do a case Insensitive string comparison.

   compare-op  can be one of
                EQU : Equal
                NEQ : Not equal

                LSS : Less than <
                LEQ : Less than or Equal <=

                GTR : Greater than >
                GEQ : Greater than or equal >=

                This 3 digit syntax is necessary because the > and <
                symbols are recognised as redirection operators

IF will only parse numbers when one of (EQU, NEQ, LSS, LEQ, GTR, GEQ) is used.
The == comparison operator always results in a string comparison.

ERRORLEVEL

There are two different methods of checking an errorlevel, the first syntax ( IF ERRORLEVEL … ) provides compatibility with ancient batch files from the days of Windows 95.
The second method is to use the %ERRORLEVEL% variable providing compatibility with Windows 2000 or newer.

IF ERRORLEVEL n statements should be read as IF Errorlevel >= number
i.e.
IF ERRORLEVEL 0 will return TRUE whether the errorlevel is 0, 1 or 5 or 64
IF ERRORLEVEL 1 will return TRUE whether the errorlevel is 1 or 5 or 64
IF NOT ERRORLEVEL 1 means if ERRORLEVEL is less than 1 (Zero or negative).
This is not very readable or user friendly and does not easily account for negative error numbers.

Using the %ERRORLEVEL% variable is a more logical method of checking Errorlevels:

IF %ERRORLEVEL% NEQ 0 Echo An error was found
IF %ERRORLEVEL% EQU 0 Echo No error found

IF %ERRORLEVEL% EQU 0 (Echo No error found) ELSE (Echo An error was found)
IF %ERRORLEVEL% EQU 0 Echo No error found || Echo An error was found

This allows you to trap errors that can be negative numbers, you can also test for specific errors:
IF %ERRORLEVEL% EQU 64 …

To deliberately raise an ERRORLEVEL in a batch script use the EXIT /B command.

It is possible (though not a good idea) to create a string variable called %ERRORLEVEL% (user variable)
if present such a variable will prevent the real ERRORLEVEL (a system variable) from being used by commands such as ECHO and IF.

Test if a variable is empty

To test for the existence of a command line parameter – use empty brackets like this

IF [%1]==[] ECHO Value Missing
or
IF [%1] EQU [] ECHO Value Missing

When comparing against a variable that may be empty, we include a pair of brackets [ ] so that if the variable does happen to be empty the IF command still has something to compare: IF [] EQU [] will return True.

You can in fact use almost any character for this a ‘~’ or curly brackets, { } or even the number 4, but square brackets tend to be chosen because they don’t have any special meaning.
When working with filenames/paths you should always surround them with quotes, if %_myvar% contains “C:\Some Path” then your comparison becomes IF [“C:\Some Path”] EQU []
if %_myvar% could contain empty quotes, “” then your comparison should become IF [%_myvar%] EQU [“”]

if %_myvar% will never contain quotes, then you can use quotes in place of the brackets IF “%_myvar%” EQU “”
However with this pattern if %_myvar% does unexpectedly contain quotes, you will get IF “”C:\Some Path”” EQU “” those doubled quotes, while not officially documented as an escape will still mess up the comparison.

Test if a variable is NULL

In the case of a variable that might be NULL – a null variable will remove the variable definition altogether, so testing for a NULL becomes:

IF NOT DEFINED _example ECHO Value Missing

IF DEFINED will return true if the variable contains any value (even if the value is just a space)

To test for the existence of a user variable use SET VariableName, or IF DEFINED VariableName

Test the existence of files and folders

IF EXIST filename   Will detect the existence of a file or a folder.

The script empty.cmd will show if the folder is empty or not (this is not case sensitive).

Parenthesis

Parenthesis can be used to split commands across multiple lines. This enables writing more complex IF… ELSE… commands:

IF EXIST filename.txt (
    Echo deleting filename.txt
    Del filename.txt
 ) ELSE ( 
    Echo The file was not found.
 )

When combining an ELSE statement with parentheses, always put the opening parenthesis on the same line as ELSE.
 ) ELSE (   This is because CMD does a rather primitive one-line-at-a-time parsing of the command.

When using parentheses the CMD shell will expand [read] all the variables at the beginning of the code block and use those values even if the variables value has just been changed. Turning on DelayedExpansion will force the shell to read variables at the start of every line.

Pipes

When piping commands, the expression is evaluated from left to right, so

IF SomeCondition Command1 | Command2is equivalent to:

(IF SomeCondition Command1 ) | Command2
The pipe is always created and Command2 is always run, regardless whether SomeCondition is TRUE or FALSE

You can use brackets and conditionals around the command with this syntax:

IF SomeCondition (Command1 | Command2)
If the condition is met then Command1 will run, and its output will be piped to Command2.

The IF command will interpret brackets around a condition as just another character to compare (like # or @) for example:
IF (%_var1%==(demo Echo the variable _var1 contains the text demo

Placing an IF command on the right hand side of a pipe is also possible but the CMD shell is buggy in this area and can swallow one of the delimiter characters causing unexpected results.
A simple example that does work:

Echo Y | IF red==blue del *.log

Chaining IF commands (AND).

The only logical operator directly supported by IF is NOT, so to perform an AND requires chaining multiple IF statements:

IF SomeCondition (
   IF SomeOtherCondition (
     Command_if_both_are_true
   )
)

If either condition is true (OR)

This can be tested using a temporary variable:

Set “_tempvar=”
If SomeCondition Set _tempvar=1
If SomeOtherCondition Set _tempvar=1
if %_tempvar% EQU 1 Command_to_run_if_either_is_true

Delimiters

If the string being compared by an IF command includes delimiters such as [Space] or [Comma], then either the delimiters must be escaped with a caret ^ or the whole string must be “quoted”.
This is so that the IF statement will treat the string as a single item and not as several separate strings.

Test Numeric values

IF only parses numbers when one of the compare-op operators (EQU, NEQ, LSS, LEQ, GTR, GEQ) is used.
The == comparison operator always results in a string comparison.

This is an important difference because if you compare numbers as strings it can lead to unexpected results: “2” will be greater than “19” and “026” will be less than “10”.

Correct numeric comparison:
IF 2 GEQ 15 echo “bigger”

Using parentheses or quotes will force a string comparison:
IF (2) GEQ (15) echo “bigger”
IF “2” GEQ “15” echo “bigger”

This behaviour is exactly opposite to the SET /a command where quotes are required.

IF should work within the full range of 32 bit signed integer numbers (-2,147,483,648 through 2,147,483,647)

C:\> if 2147483646 GEQ 2147483647 (Echo Larger) Else (Echo Smaller)
Smaller   ⇨ correct

C:\> if 2147483647 GEQ 2147483648 (Echo Larger) Else (Echo Smaller)
Larger   ⇨ wrong due to overflow

C:\> if -2147483649 GEQ -2147483648 (Echo Larger) Else (Echo Smaller)
Larger   ⇨ wrong due to overflow

You can perform a string comparison on very long numbers, but this will only work as expected when the numbers are exactly the same length:

C:\> if “2147483647” GEQ “2147483648” (Echo Larger) Else (Echo Smaller)
Smaller   ⇨ correct

Wildcards

Wildcards are not supported by IF, so %COMPUTERNAME%==SS6* will not match SS64

A workaround is to retrieve the substring and compare just those characters:
SET _prefix=%COMPUTERNAME:~0,3%
IF %_prefix%==SS6 GOTO they_matched

If Command Extensions are disabled IF will only support direct comparisons: IF ==, IF EXIST, IF ERRORLEVEL
also the system variable CMDEXTVERSION will be disabled.

IF does not, by itself, set or clear the Errorlevel.

Examples:

IF EXIST C:\logs\*.log (Echo Log file exists)

IF EXIST C:\logs\install.log (Echo Complete) ELSE (Echo failed)

IF DEFINED _department ECHO Got the _department variable

IF DEFINED _commission SET /A _salary=%_salary% + %_commission% 

IF CMDEXTVERSION 1 GOTO start_process

IF %ERRORLEVEL% EQU 2 goto sub_problem2

IF is an internal command.