Detect if you're running in a cmd.exe subshell

test-subshell.bat

@echo off

setlocal EnableDelayedExpansion

:: Dequote path to command processor and this script path
set ScriptPath=%~0
set CmdPath=%COMSPEC:"=%

:: Get command processor filename and filename with extension
for %%c in (!CmdPath!) do (
    set CmdExeName=%%~nxc
    set CmdName=%%~nc
)

:: Get this process' PID
:: Adapted from: http://www.dostips.com/forum/viewtopic.php?p=22675#p22675
set "uid="
for /l %%i in (1 1 128) do (
    set /a "bit=!random!&1"
    set "uid=!uid!!bit!"
)

for /f "tokens=2 delims==" %%i in (
    'wmic Process WHERE "Name='!CmdExeName!' AND CommandLine LIKE '%%!uid!%%'" GET ParentProcessID /value'
) do (
    rem Get commandline of parent
    for /f "tokens=1,2,*" %%j in (
        'wmic Process WHERE "Handle='%%i'" GET CommandLine /value'
    ) do (

        rem Strip extra CR's from wmic output
        rem http://www.dostips.com/forum/viewtopic.php?t=4266
        for /f "delims=" %%x in ("%%l") do (
            rem Dequote path to batch file, if any (3rd argument)
            set ParentScriptPath=%%x
            set ParentScriptPath=!ParentScriptPath:"=!
        )

        rem Get parent process path
        for /f "tokens=2 delims==" %%y in ("%%j") do (
            rem Dequote parent path
            set ParentPath=%%y
            set ParentPath=!ParentPath:"=!

            rem Handle different invocations: C:\Windows\system32\cmd.exe , cmd.exe , cmd
            for %%p in (!CmdPath! !CmdExeName! !CmdName!) do (
                if !ParentPath!==%%p set IsCmdParent=1
            )

            rem Check if we're running in cmd.exe with /c switch and this script path as argument
            if !IsCmdParent!==1 if %%k==/c if "!ParentScriptPath!"=="%ScriptPath%" set IsExternal=1
        )
    )
)

if !IsExternal!==1 (
    echo %~nx0 only works if run directly from !CmdExeName!^^!
    exit 1
) else (
     echo Running interactively in !CmdExeName! session.
 )

endlocal