Windows Batch判断变量是否定义

@echo off

if defined MYVAR (
   echo ERROR: MYVAR is defined
) else (
   echo ERROR: MYVAR is not defined
)

if not defined MYVAR (
   echo MYVAR is not defined
) else (
   echo MYVAR is defined
)

运行:

C:\> set MYVAR=<avalue>
C:\> test.bat
MYVAR is defined
MYVAR is defined

C:\> set MYVAR=
C:\> test.bat
MYVAR is defined
MYVAR is defined