Question

I’m getting strange behavior in variable assignment in a batch script that I’ve written. The simplest example I could concoct to re-create the problem follows. I created the file type pos.bat:

@echo on
FOR /R ".\" %%F IN (*.txt) DO (
echo Look: %%F
set file=%%~dpF%%~nF
echo %file%
)

In a directory containing two *.txt files, with one in a subdirectory:

pos/
    |-pos.bat
    |-file1.txt
    |dir/
         |-file2.txt

I get the following output:

F:\pos>pos.bat
F:\pos>FOR /R ".\" %F IN (*.txt) DO (
echo Look: %F
 set file=%~dpF%~nF
 echo F:\pos\dir\file2
)

F:\pos>(
echo Look: F:\pos\file1.txt
 set file=F:\pos\file1
 echo F:\pos\dir\file2
)
Look: F:\pos\file1.txt
F:\pos\dir\file2

F:\pos>(
echo Look: F:\pos\dir\file2.txt
 set file=F:\pos\dir\file2
 echo F:\pos\dir\file2
)
Look: F:\pos\dir\file2.txt
F:\pos\dir\file2

Shouldn’t the value of %file% change back to F:\pos\file1.txt on the first iteration of the loop? Also, I was surprised that the value of `%file% should persist at all between calls to the script. The first call to the script behaved as I intended:

F:\pos>FOR /R ".\" %F IN (*.txt) DO (
echo Look: %F
 set file=%~dpF%~nF
 echo
)

F:\pos>(
echo Look: F:\pos\file1.txt
 set file=F:\pos\file1
 echo
)
Look: F:\pos\file1.txt
ECHO is on.

F:\pos>(
echo Look: F:\pos\dir\file2.txt
 set file=F:\pos\dir\file2
 echo
)
Look: F:\pos\dir\file2.txt
ECHO is on.

But all subsequent calls give me garbage results. Any help is greatly appreciated.

Answer 1

You need to enable delayed expansion and then use ! for the variable within the loop.

At the top of your file (typically)

SETLOCAL EnableDelayedExpansion

Within your FOR loop

echo !file!

Here’s a good resource on the why’s and wherefore’s.