How to survive "delayed variable expansion" in a Windows batch script - windows

Question

This is my script:
#echo off
setlocal
for /f %%i in ('echo aaa/') do set REPO=%%i
if "%REPO%"=="" (
echo No input
) else (
echo %REPO:~-1%
echo %REPO:~0,-1%
if %REPO:~-1%==/ set REPO=%REPO:~0,-1%
echo %REPO%
)
endlocal
Please, observe:
c:\dev\shunra\GlobalLibrary\Server>c:\Utils\hgbackup.cmd
/
aaa
aaa/
c:\dev\shunra\GlobalLibrary\Server>
What is going on?
EDIT
Note, that I am assigning to REPO something that evaluates to "aaa", hence I expect it to print "aaa", not "aaa/". It drives me crazy.
EDIT2
Apparently, here is the culprit (from help on the set command):
Finally, support for delayed environment variable expansion has been
added. This support is always disabled by default, but may be
enabled/disabled via the /V command line switch to CMD.EXE. See CMD /?
Delayed environment variable expansion is useful for getting around
the limitations of the current expansion which happens when a line
of text is read, not when it is executed. The following example
demonstrates the problem with immediate variable expansion:
set VAR=before
if "%VAR%" == "before" (
set VAR=after
if "%VAR%" == "after" #echo If you see this, it worked
)
would never display the message, since the %VAR% in BOTH IF statements
is substituted when the first IF statement is read, since it logically
includes the body of the IF, which is a compound statement. So the
IF inside the compound statement is really comparing "before" with
"after" which will never be equal. Similarly, the following example
will not work as expected:
set LIST=
for %i in (*) do set LIST=%LIST% %i
echo %LIST%
in that it will NOT build up a list of files in the current directory,
but instead will just set the LIST variable to the last file found.
Again, this is because the %LIST% is expanded just once when the
FOR statement is read, and at that time the LIST variable is empty.
So the actual FOR loop we are executing is:
for %i in (*) do set LIST= %i
which just keeps setting LIST to the last file found.
Delayed environment variable expansion allows you to use a different
character (the exclamation mark) to expand environment variables at
execution time. If delayed variable expansion is enabled, the above
examples could be written as follows to work as intended:
set VAR=before
if "%VAR%" == "before" (
set VAR=after
if "!VAR!" == "after" #echo If you see this, it worked
)
set LIST=
for %i in (*) do set LIST=!LIST! %i
echo %LIST%
But I tried using the ! sign, still it does not work for me. I use get ! printed on the screen or the wrong result again.

Answer 1

As has been discussed in the comments, and in your edited question, you need delayed expansion.
Delayed expansion must be enabled before you can use it. Within a batch script you can use setlocal enableDelayedExpansion
#echo off
setlocal enableDelayedExpansion
for /f %%i in ('echo aaa/') do set REPO=%%i
if "%REPO%"=="" (
echo No input
) else (
echo %REPO:~-1%
echo %REPO:~0,-1%
if %REPO:~-1%==/ set REPO=%REPO:~0,-1%
echo !REPO!
)
endlocal
EDIT
The above fails if the IN() clause is changed such that REPO is undefined. For example: in (echo.)
It fails because the entire IF/ELSE construct must have valid syntax, even it the ELSE clause will not be executed.
If REPO is undefined, then
if %REPO:~-1%==/ set REPO=%REPO:~0,-1%
expands to
if ~-1REPO:~0,-1
which is invalid syntax.
The problem again is solved by using delayed expansion.
#echo off
setlocal enableDelayedExpansion
for /f %%i in ('echo.') do set REPO=%%i
if "%REPO%"=="" (
echo No input
) else (
echo %REPO:~-1%
echo %REPO:~0,-1%
if !REPO:~-1!==/ set REPO=%REPO:~0,-1%
echo !REPO!
)
endlocal

Answer 2

Note, that I am assigning to REPO something that evaluates to "aaa"
Actually, you're conditionally assigning something. Have you testing whether the then-part is actually executing (for example, echo If Entered).

Answer 3

This works for me (just an extract from my whole script)
choice /C 1234567H /M "Select an option or ctrl+C to cancel"
set _dpi=%ERRORLEVEL%
if "%_dpi%" == "8" call :helpme && goto menu
for /F "tokens=%_dpi%,*" %%1 in ("032 060 064 096 0C8 0FA 12C") do set _dpi=%%1
echo _dpi:%_dpi%: