windows - 为什么递归 (/R) for 循环在 Windows 批处理文件中有奇怪的行为

Question

似乎 !DRIVE!考虑到延迟扩展已启用，应该可以工作。为什么不呢？为什么下面的代码不适用于第一种情况？

@echo off
setlocal EnableDelayedExpansion
SET "DRIVE=H:\"

REM DOESN'T WORK
FOR /R "!DRIVE!" %%S in (*) do (
    echo(%%S
)
pause

REM WORKS
FOR /R "%DRIVE%" %%S in (*) do (
    echo(%%S
)
pause

REM WORKS
FOR /R "H:\" %%S in (*) do (
    echo(%%S
)
pause

Answer 1

因为... that's how it works (for/f 选项也有这个问题)。 For 有一个单独的解析器并且 for 定义不受延迟扩展的影响(尝试不使用 echo off 以查看执行的内容)。您可以使用两种解决方法之一(使用子例程)

@echo off
setlocal EnableDelayedExpansion
SET "DRIVE="H:\""
call :rec !DRIVE!
exit /b 0


:rec
FOR /R "%~1" %%S in (*) do (
    echo(%%S
)

(嵌套for)

@echo off
setlocal EnableDelayedExpansion
SET "DRIVE=H:\"

set "cmd=for /R "%%DRIVE%%" %%a in (*) do @echo(%%a"

for /F "delims=" %%x in ('!cmd!') do echo %%x