batch file fails to set variable in IF clause

Question

The following code is not updating Run to equal N even though the match occurs. this means I\'m not dropping into the CALL code. Am i missing something here?

Answer 1

You need to use the delayed expansion option of cmd.exe.

At the top of your script, put:

setlocal enableextensions enabledelayedexpansion

and then put:

endlocal

at the bottom.

Then you need to use !Run! instead of %Run%.

The reason your code is not working is that the entire FOR statement (including the commands within it) is evaluated when it's encountered. That's the point where the %Run% variables are expanded.

By using deferred expansion, you don't expand them until they're actually needed (after you've set them within the block).

You can see the difference in this script:

@echo off
setlocal enableextensions enabledelayedexpansion

set xx=0
for %%i in (a b c d) do (
    echo %%i
    set /a "xx = xx + 1"
    if %xx%==3 echo yes for normal
    if !xx!==3 echo yes for delayed
)

endlocal

which outputs:

a
b
c
yes for delayed
d

You'll notice that the check with %xx% does not work because that was evaluated when the for statement started (and xx was 0). The delayed-expansion !xx! does work since that is evaluated each time through the loop.