bat是否在for循环不能改变变量的值?

@echo off
setlocal enabledelayedexpansion
set flag=1
(for /f "tokens=1* delims=:" %%h in ('findstr /n "." "my.txt"') do (
set "str=%%i"
echo %flag%
if %flag%==1 (
set flag=0
) else (
echo,%%i
)
))
为什么flag一直都是1啊

相关了解……