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] [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 used 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.
The IF command can seem flaky if any spaces exist in the comparison strings. for example these commands all seem like they work:
IF 'ab' == 'a b' Echo OK
IF [ab] == [a b] Echo OKBut if you reverse the logic to see if they are not equal, the code will fail and thow an error:
IF 'ab' NEQ 'a b' Echo OK
IF [ab] NEQ [a b] Echo OKSimilarly this will fail:
IF 'a b' == 'a b' Echo OK
The problem with the above, is that single quotes have no special meaning to CMD, so when it reaches a space it assumes that’s the end of the string.
These versions using double quotes will all work:
IF "ab" == "a b" Echo OK
IF "ab" NEQ "a b" Echo OK
IF NOT "ab" == "a b"So then you think, OK I’ll just use double quotes. However there is one remaining gotcha, if the item you are comparing is a quoted filename, so it already contains double quotes, you have an escape sequence:
IF ""long filename"" EQU "something" Echo OK
That will break because the "" acts as an escape. To prevent that from happening strip any quotes from the strings being compared.
In addition to spaces, the above applies to all other delimiters [Comma],[Semicolon], [Equals], [Space] [Tab].
Either the delimiters must be individually escaped with a caret ^ or the whole string must be "quoted".
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, act as an escape and will break the comparison.
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 variable use SET VariableName, or IF DEFINED VariableName
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 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.
When piping commands, the expression is evaluated from left to right, so
IF SomeCondition Command1 | Command2 is equivalent to:
(IF SomeCondition Command1 ) | Command2
The pipe is always created and Command2 is always run, regardless whether SomeCondition is TRUE or FALSEYou 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 demoPlacing 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.
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 ) )
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
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 ⇨ correctC:\> if 2147483647 GEQ 2147483648 (Echo Larger) Else (Echo Smaller)
Larger ⇨ wrong due to overflowC:\> if -2147483649 GEQ -2147483648 (Echo Larger) Else (Echo Smaller)
Larger ⇨ wrong due to overflowYou 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 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
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 available in 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 foundThis 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 override and prevent the system variable %ERRORLEVEL% from being read by commands such as ECHO and IF.
If Command Extensions are disabled IF will only support direct comparisons: IF ==, IF EXIST, IF ERRORLEVEL
also the system variable CMDEXTVERSION will be disabled.
In early versions of Windows NT/XP comparisons made using == would include the spaces before and after the ==, so for backwards compatibility you may still see commands written as IF alpha==beta rather than IF alpha == beta
IF does not, by itself, set or clear the Errorlevel.
IF is an internal command.
Does a specific file exist:
IF EXIST C:\logs\install.log (Echo Complete) ELSE (Echo failed)
Does any file exist:
IF EXIST C:\logs\*.log (Echo Log file exists)
Does a variable exist:
IF DEFINED _department ECHO This is for %_department%.
IF DEFINED _commission SET /A "_salary=%_salary% %_commission%"
Do we have Command Processor Extensions set?
IF CMDEXTVERSION 2 GOTO start_process
Does an error exist:
IF %ERRORLEVEL% EQU 2 goto sub_problem2
You see things; and you say 'Why?' But I dream things that never were; and I say 'why not?' ~ George Bernard Shaw
Using parentheses to group and expand expressions.
Conditional execution syntax (AND / OR)
SET - Display or Edit environment variables.
ECHO - Display message on screen.
EXIT - Set a specific ERRORLEVEL.
IFMEMBER - group member (Resource kit).
SC - Is a Service running (Resource kit).
Equivalent PowerShell: IF - Conditionally perform a command.
Equivalent bash command (Linux):
if - Conditionally perform a command.