Start new cmd.exe and NOT inherit environment?

Question

If I start a new CMD shell from an existing shell, the new shell inherits the existing environment. Is there a way to start a new shell but have it initialized to the system defaults and not inherit?

Current result:

B:\>set _test=blooharky

B:\>cmd
Microsoft Windows [Version 6.1.7600]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

B:\>set _
_test=blooharky

Desired result:

B:\>set _test=blooharky

B:\>cmd /env=default
Microsoft Windows [Version 6.1.7600]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

B:\>set _
Environment variable _ not defined

[update] Solution for this is start /i cmd, as shared by dbenham, below. However it doesn't help in the situation where the current shell is already second generation. Example:

d:\>set _
Environment variable _ not defined

d:\>set _test=blooharky

d:\>cmd /k

:: some work done using _test here...
:: ...but after we need a new clean shell:

d:\>start /i cmd

d:\>set _
_test=blooharky

:: uhoh, our shell isn't clean!

Answer 1

Anders' recipe has detailed control over a new environment, and I'm leaving that as the accepted answer because of that depth control. However one phrase in that answer led to me the method I'll actually be using for the particular problem which prompted this enquiry. An "environment that is equal to the initial explorer.exe environment". Oh! I know how to do that!

start /i "%windir%\explorer.exe" "%windir%\system32\cmd.exe"

Note: originally this was simply start /i explorer ..., but it turns out that doesn't work reliably, and a full path should be be used for both parts. If all you need is a solution, you have everything now and can ignore the rest.

---

Following Ander's comment below about a security warning I tested on 4 Win7 computers, a mix of Pro, Home, and Enterprise, 32 and 64bit. I fiddled with User Account Control, all the way up and all the way down. Also tested with a non-administrator Command Prompt shell. These all worked without error or warning.

On Server 2003, logged on as local administrator, I get a popup dialog "File Download - Security Warning: do you want to run or save this file?" with buttons for run,save, and cancel. Pressing [run] results in an additional dialog, "Windows Explorer - Security Warning: the publisher could not be verified. Are you sure you want to run this software?". Pressing [run] again finally results in a usable command shell. Apparently there is some weird logic that results in Internet Explorer being substituted for Windows Explorer without the full path to the exe.

It gets even stranger though: using start with a title, (some advise to always include a title) results in the security warnings regardless of full path. Other parameters like starting directory seem to be okay.

:: security warning
start "clean shell" /i "%windir%\explorer.exe" "%windir%\system32\cmd.exe"

:: is okay
start /i  /d x:\ "%windir%\explorer.exe" "%windir%\system32\cmd.exe"

Answer 2

If you're willing to use powershell, you can use:

Start-Process -UseNewEnvironment powershell

or

Start-Process -UseNewEnvironment cmd

Answer 3

Some of the variables are initialized at logon and are not stored with the other registry entries so if you want a environment that is equal to the initial explorer.exe environment you need to white-list those items and hope they have not been changed by anyone:

@echo off
setlocal ENABLEEXTENSIONS DISABLEDELAYEDEXPANSION
goto main

:SetFromReg
FOR /F "tokens=2,*" %%A IN ('REG query "%~1" /v "%~2"^|find /I "REG_"') DO (
    call set %~3=%%B
)
goto :EOF

:GetRegEnv
FOR /F %%A IN ('REG query "%~1" /s^|find /I "REG_"') DO (
    if /I not "%%~A"=="Path" call :SetFromReg "%~1" "%%~A" "%%~A"
)
goto :EOF

:InheritOrDelete
for %%A in (save_TEMP Path SystemRoot SystemDrive ProgramFiles CommonProgramFiles ALLUSERSPROFILE COMPUTERNAME LOGONSERVER USERNAME USERDOMAIN HOMEDRIVE HOMEPATH USERPROFILE APPDATA) do if /I "%%~A"=="%~1" goto :EOF
set %~1=
goto :EOF

:main
REM Save temp
set save_TEMP=%temp%
if not defined save_TEMP set save_TEMP=%tmp%

for /F "delims==" %%A in ('set') do call :InheritOrDelete "%%~A"
call :GetRegEnv "HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Environment"
call :GetRegEnv "HKCU\Environment"

REM Special handling for Path
call :SetFromReg "HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Environment" Path Path
setlocal
set u=
call :SetFromReg "HKCU\Environment" Path u
endlocal&if not "%Path%"=="" if not "%u%"=="" set Path=%Path%;%u%

REM Restore TEMP/TMP
set TEMP=%save_TEMP%
set save_TEMP=
set TMP=%TEMP%

REM start some command...
start cmd /d /k set

The output from reg.exe is not the same on every windows version so you would have to make sure that it works on your target system (It will also have problems if the name of a variable contains a space, you could fix that by replacing "tokens=2,*" with "tokens=2,* delims= " (delims equals tab) but before you do that make sure that the reg.exe output always uses tab as the separator)

You can work around these issues by using a windows scripting host script instead of a batch file:

'orgenvshell.vbs:
Set WShl = CreateObject( "WScript.Shell" )
Set FSO = CreateObject("Scripting.FileSystemObject")

Function CanInherit(n)
    CanInherit = False
    w = Split("SystemRoot SystemDrive ProgramFiles CommonProgramFiles ALLUSERSPROFILE COMPUTERNAME LOGONSERVER USERNAME USERDOMAIN HOMEDRIVE HOMEPATH USERPROFILE APPDATA")
    For Each i In w
        If 0 = StrComp(i,n,1) Then
            CanInherit = True
            Exit Function
        End If
    Next
End Function

Function GetShortFolderPath(p)
    GetShortFolderPath = p
    On Error Resume Next
    GetShortFolderPath = FSO.GetFolder(p).ShortPath
End Function

Sub E(dst,src)
    set envs = WShl.Environment(src)
    For Each i In envs
        t = Split(i,"=")
        n = t(0)
        If n = "" Then n = "="&t(1)
        If IsNull(dst) Then
            If not CanInherit(n) Then envs.Remove n
        Else
            v = Mid(i,Len(n)+2)
            envd = dst
            If "X" = dst Then
                v = WShl.ExpandEnvironmentStrings(v)
                envd = src
                If 0 = StrComp(n,"TMP",1) Then v = GetShortFolderPath(v)
                If 0 = StrComp(n,"TEMP",1) Then v = GetShortFolderPath(v)
            End If
            WShl.Environment(envd)(n) = v
        End If
    Next
End Sub

E Null,"PROCESS"
E "PROCESS","SYSTEM"
E "PROCESS","USER"
E "X","PROCESS"

'Special hack for Path
s = WShl.Environment("SYSTEM")("Path")
u = WShl.Environment("USER")("Path")
If Len(u) Then s = s&";"&u
WShl.Environment("PROCESS")("Path") = WShl.ExpandEnvironmentStrings(s)

'Test a command
WShl.Run "cmd /d /k set ",1

You could probably remove a lot of the white-listed items by querying WMI and using other WSH methods...

Answer 4

I'm not aware of a way to do it in the same window. But you can accomplish the task in a separate window using

start /i cmd

If you want your current cmd session to wait until the new session ends you can add the /wait option

EDIT

I stand corrected, thanks to Romário's comment. You can add the /B and /WAIT options to create the new cmd.exe session in the same window.

start /i /b /wait cmd

Note that the new cmd.exe inherits the initial environment that existed when the parent was launched. It may not be the default environment if the parent was itself launched from another cmd.exe environment.

Answer 5

A sample below of how I got this working for me.

@ECHO OFF
TITLE Test
SET SELF=%~dp0%~n0%~x0

ECHO SetVar : %VAR1%
PAUSE
SETX VAR1 "Random Value"
WMIC PROCESS CALL CREATE "%SELF%"
EXIT 0

Answer 6

This looks like an old post, but this is what I tried:

start /i

this link has more info: http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/start.mspx?mfr=true

That command should open a new window which is like the startup cmd environment.