Windows – How to set the value of an environment variable to the output of a command in a WIndows batch file

The default value in Windows XP: .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH

The default value in Windows Vista, 7, 8 and 10 - have also confirmed in Server 2008 R2: .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC

If your value isn't the same as this, it's been modified, these are the default out-of-the-box values. .MSC is the only addition since Windows XP, a Microsoft Management Console Snap-in Control File, used for things such as Group Policy Editor gpedit.msc.

Further reading: Wikipedia

You could run the following batch, or a variation of it, to quickly see if they'd been changed.

@echo off
setlocal
for /f "tokens=4-5 delims=. " %%i in ('ver') do set VERSION=%%i.%%j

IF "%version%" == "5.1" GOTO windowsxp
IF "%version%" == "5.2" GOTO windowsxp

:windowsabovexp

set "PATHEXTORIGINAL=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC"

GOTO compare

:windowsxp

set "PATHEXTORIGINAL=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH"

:compare

if not "%PATHEXT%" == "%PATHEXTORIGINAL%" (
   echo PATHEXT has been modified!
) else (
   echo PATHEXT is expected!
)

Simply use the set command:

C:\>set foo=bar

C:\>echo %foo%
bar

C:\>exit

Open cmd again

C:\>echo %foo%
%foo%

C:\>