I've seen SETLOCAL ENABLEDELAYEDEXPANSION & SETLOCAL DISABLEDELAYEDEXPANSION in many batch files but what do the commands actually do?
4 Answers
enabledelayeexpansion instructs cmd to recognise the syntax !var! which accesses the current value of var. disabledelayedexpansion turns this facility off, so !var! becomes simply that as a literal string.
Within a block statement (a parenthesised series of statements), the entire block is parsed and then executed. Any %var% within the block will be replaced by that variable's value at the time the block is parsed - before the block is executed - the same thing applies to a FOR ... DO (block).
Using !var! in place of %var% accesses the changed value of var.
Copied from How do you use SETLOCAL in a batch file? (as dbenham indicated in his first comment).
Suppose this code:
If "%getOption%" equ "yes" ( set /P option=Enter option: echo Option read: %option% ) Previous code will NOT work becase %option% value is replaced just one time when the IF command is parsed (before it is executed). You need to "delay" variable value expansion until SET /P command had modified variable value:
setlocal EnableDelayedExpansion If "%getOption%" equ "yes" ( set /P option=Enter option: echo Option read: !option! ) Check this:
set var=Before set var=After & echo Normal: %var% Delayed: !var! The output is: Normal: Before Delayed: After
With delayed expansion you will able to access a command argument using FOR command tokens:
setlocal enableDelayedExpansion set /a counter=0 for /l %%x in (1, 1, 9) do ( set /a counter=!counter!+1 call echo %%!counter! ) endlocal Can be useful if you are going to parse the arguments with for loops
It helps when accessing variable through variable:
@Echo Off Setlocal EnableDelayedExpansion Set _server=frodo Set _var=_server Set _result=!%_var%! Echo %_result% And can be used when checking if a variable with special symbols is defined:
setlocal enableDelayedExpansion set "dv==::" if defined !dv! ( echo has NOT admin permissions ) else ( echo has admin permissions ) ALSO note that with SETLOCAL ENABLEDELAYEDEXPANSION you cant echo !!!!!! so:
echo my sentence! 123 will be outputed as:
my sentence 123
