Windows Batch For循环未按预期重复执行的问题排查

问题原因 #

for /F 循环的核心机制是先完整读取并解析循环的输入源，再启动迭代流程。你这里的输入源是 "!my_str!"，循环启动时就已经把初始的my_str内容解析完毕，只会提取第一个符合delims规则的子串（也就是I am A）。之后在循环体里修改my_str的值，完全不会改变循环一开始就确定好的迭代次数和处理内容，所以循环只执行了一次。

解决方法 #

因为子串数量未知，我们可以用goto模拟while循环的逻辑，反复切割字符串直到my_str为空：

@echo off
setlocal enabledelayedexpansion

set "my_delim=`"
set "my_str=I am A`I am B`I am C`"

:loop
if not "!my_str!"=="" (
    for /F "delims=%my_delim%" %%A in ("!my_str!") do (
        echo inside loop started
        echo A value is [%%A]
        
        set "my_str=!my_str:*%my_delim%=!"
        echo remaining my_str is [!my_str!]
        echo inside loop ended
        echo ------------------------------------
    )
    goto loop
)
echo exited loop
pause

效果验证 #

运行修改后的脚本，会完全匹配你预期的输出：

inside loop started
A value is [I am A]
remaining my_str is [I am B`I am C`]
inside loop ended
------------------------------------
inside loop started
A value is [I am B]
remaining my_str is [I am C`]
inside loop ended
------------------------------------
inside loop started
A value is [I am C]
remaining my_str is []
inside loop ended
------------------------------------
exited loop
Press any key to continue . . . 

内容的提问来源于stack exchange，提问作者Grace