Delayed variable expansion inside a substring operation

Question

SETLOCAL EnableDelayedExpansion

SET str=123456789abcdefgh

FOR /l %%x IN (1, 1, 10) DO (

    SET /a intLength=10-%%x

    SET result=!str:~-%%x!
    ECHO "Works as intended: " !result!

    SET result=!str:~-intLength!
    ECHO "Does NOT work as intended: " !result!
)

endlocal

Answer 1

You're using the literal string intLength instead of the %intLength% variable.

Since you're initializing a variable inside of a for loop, you're going to have to use the !intLength! variation of this variable name. Unfortunately, since you're already using exclamation points to get the substring from str , you can't also use them in that line to get the value of intLength , since you'd then essentially have a variable !str:~! , an unrelated string that batch really isn't going to like, and a !! .

You can get around this by running !intLength! through another for loop and using the %%var variable instead, since you've already shown that that works.

@echo off
setlocal EnableDelayedExpansion

set str=123456789abcdefgh

for /l %%x in (1, 1, 10) DO (

    set /a intLength=10-%%x

    SET result=!str:~-%%x!
    echo Works as intended: !result!

    for /f %%A in ("!intLength!") do SET result=!str:~-%%A!
    echo Now works as intended: !result!
    echo.
)

endlocal