问题
Below is my script. I am trying to look into folders one level below and pick out only those folders, hence the ~-9 which extracts the last 9 chars from the path. But the set var= does not unset the variable because the output comes back with the same folder name repeated # times. Also batch doesn't allow me to do this extract trick directly on %%i, hence the need for the local variable.
How do I clear this variable so that it takes the new value in the next iteration?
@echo off
for /d %%i in (%1\*) do (
set var=%%i
echo %var:~-9%
set "var="
)
回答1:
http://judago.webs.com/variablecatches.htm has an explanation for my problem. The magic lines were setlocal enabledelayedexpansion and calling var as echo !var:~-9!. ! vs % ...wow! cmd still amazes me.
回答2:
You found the source of your problem, as well as the solution - delayed expansion.
But using FOR while delayed expansion is enabled can cause problems if any of the filenames contain the ! character. The expansion of the for variable %%i will be corrupted if the value contains ! and delayed expansion is enabled. This is not a frequent problem, but it happens.
The solution is to toggle delayed expansion on and off within the loop
@echo off
setlocal disableDelayedExpansion
for /d %%i in (%1\*) do (
set var=%%i
setlocal enableDelayedExpansion
echo !var:~-9!
endlocal
)
I'm also wondering what you mean by "I am trying to look into folders one level below and pick out only those folders, hence the ~-9 which extracts the last 9 chars from the path". I suspect your are trying to get the name of the child folder, without the leading path information. If that is so, then using the substring operation is not a good solution because the length of folder names varies.
There is a very simple method to get the name of the folder without the leading path info:
for /d %%i in (%1\*) do echo %%~nxi
来源：https://stackoverflow.com/questions/11440413/batch-script-variable-unset-in-for-loop-has-no-effect