启用S​​ETLOCAL时如何在IF子句中回显环境变量

Question

如何“回显”应该扩展环境变量本身的（环境）变量的值？

示例BAT：

echo OFF
SETLOCAL

echo running test ...

set /a "YesPleaseContinue=0"
IF defined windir (
   set /a "YesPleaseContinue=1"
)

IF %YesPleaseContinue% GEQ 1 (
   set MyCustomVar=%WinDir%\System32\regsvr32.exe
   echo DEBUG1: %MyCustomVar%
) ELSE (
   echo condition not met
)

echo DEBUG2: %MyCustomVar%

timeout 120

这将产生以下输出：

running test ...
DEBUG1:
DEBUG2: C:\WINDOWS\System32\regsvr32.exe

为什么“ echo”在带有“ DEBUG1”的行中输出 empty 内容？