Batch file using variables for substring inside for loop

Question

I'm attempting to use a .bat file here and can't quiet get my desired results.

Here's the problem spot:

setlocal enabledelayedexpansion
REM Import our message
set messagelines=0
for /F "tokens=*" %%B in (Myfile.txt) do (
    SET /A messagelines=!messagelines! + 1
    set message!messagelines!=%%B
)
set message

for /L %%C in (1,1,%templatelines%) do (

    REM template%%C defined above
    call :strlen length template%%C

    set string=!message%%C!

    echo !length!

    set string=!string:~0,3!

    REM **** DOESNT WORK ****
    set string=!string:~0,!length!!

    echo !string!
)

REM Finish
exit 1


:strlen <resultVar> <stringVar>
(   
    setlocal EnableDelayedExpansion
    set "s=!%~2!#"
    set "len=0"
    for %%P in (4096 2048 1024 512 256 128 64 32 16 8 4 2 1) do (
        if "!s:~%%P,1!" NEQ "" ( 
            set /a "len+=%%P"
            set "s=!s:~%%P!"
        )
    )
)
( 
    endlocal
    set "%~1=%len%"
    exit /b
)

Everything always displays properly however I am unable to use my length variable to do a substring of my message.

I've tried a few different ways and still am unclear on what to do.

Thanks in advance.

Answer 1

That line doesn't work because you've got exclamation points inside of exclamation points and batch is matching up the two left and the two right instead of the inner two and outer two. You need to run !length! through a for loop so that the variable will use % symbols:

for %%D in (!length!) do set string=!string:~0,%%D!