Windows Server Hack [Electronic resources]

Hack 9 Add, Remove, or Retrieve Environment Variables

Environment variables can easily be added, removed, or retrieved using the script in this hack.

Using VBScript to work with the Windows system environment can be pretty simple. This hack shows how to use a script to read variables, add new variables, remove variables, and recurse through all of them. Just take a look through the script and read the comments to see how to perform each task. Note that there are four types of values in the Windows Script Host (WSH) environmentSystem, User, Volatile, and Processand the script uses all of them.

By the way, this script is provided by Dudeworks (http://www.dudeworks.net). For additional resources on Windows scripting and working with the environment, see http://msdn.microsoft.com/library/default.asp?url=/library/en-us/script56l/wsProEnvironment.asp.

The Code

Type the following script into Notepad (with Word Wrap disabled) and save it with a .vbs extension as GetEnvVars.vbs:

'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
'Created by: Rob Olson - Dudeworks 
'Created on: 10/17/2001 
'Purpose: Get Environment Variables. 
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
wscript.echo "Working with the Environment: Provided by
 www.dudeworks.net"&vbcrlf&vbcrlf&strval 
'// Create an instance of the wshShell object
set WshShell = CreateObject("WScript.Shell")
'Use the methods of the object
wscript.echo "Environment.item: "& WshShell.Environment.item("WINDIR")
wscript.echo "ExpandEnvironmentStrings: "&
 WshShell.ExpandEnvironmentStrings("%windir%")
'// add and remove environment variables
'// Specify the environment type ( System, User, Volatile, or Process )
set oEnv=WshShell.Environment("System")
wscript.echo "Adding ( TestVar=Windows Script Host ) to the System " _
& "type environment"
' add a var
oEnv("TestVar") = "Windows Script Host"
wscript.echo "removing ( TestVar=Windows Script Host ) from the System " _
& "type environment"
' remove a var
oEnv.Remove "TestVar"
'// List all vars in all environment types
'//System Type
set oEnv=WshShell.Environment("System")
for each sitem in oEnv 
strval=strval & sItem &vbcrlf 
next
wscript.echo "System Environment:"&vbcrlf&vbcrlf&strval 
strval="
'//Process Type
set oEnv=WshShell.Environment("Process")
for each sitem in oEnv 
strval=strval & sItem &vbcrlf 
next
wscript.echo "Process Environment:"&vbcrlf&vbcrlf&strval 
strval="
'//User Type
set oEnv=WshShell.Environment("User")
for each sitem in oEnv 
strval=strval & sItem &vbcrlf 
next
wscript.echo "User Environment:"&vbcrlf&vbcrlf&strval 
strval="
'//Volatile Type
set oEnv=WshShell.Environment("Volatile")
for each sitem in oEnv 
strval=strval & sItem &vbcrlf 
next
wscript.echo "Volatile Environment:"&vbcrlf&vbcrlf&strval 
strval="

Running the Hack

To run the script, open a command prompt, change to the directory where the script is saved, and type cscript.exe GetEnvVars.vbs. Here is an example of typical output from the script on a Windows 2000 machine:

Microsoft (R) Windows Script Host Version 5.6
Copyright (C) Microsoft Corporation 1996-2001. All rights reserved.
Working with the Environment: Provided by www.dudeworks.net
Environment.item: %SystemRoot%
ExpandEnvironmentStrings: C:\WINNT
Adding ( TestVar=Windows Script Host ) to the System type environment
removing ( TestVar=Windows Script Host ) from the System type environment
System Environment:
ComSpec=%SystemRoot%\system32\cmd.exe
Os2LibPath=%SystemRoot%\system32\os2\dll;
Path=%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem
windir=%SystemRoot%
OS=Windows_NT
PROCESSOR_ARCHITECTURE=x86
PROCESSOR_LEVEL=6
PROCESSOR_IDENTIFIER=x86 Family 6 Model 5 Stepping 2, GenuineIntel
PROCESSOR_REVISION=0502
NUMBER_OF_PROCESSORS=1
PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH
TEMP=%SystemRoot%\TEMP
TMP=%SystemRoot%\TEMP
Process Environment:
=C:=C:=ExitCode=00000000
ALLUSERSPROFILE=C:\Documents and Settings\All Users
APPDATA=C:\Documents and Settings\Administrator\Application Data
CommonProgramFiles=C:\Program Files\Common Files
COMPUTERNAME=SNOOPY
ComSpec=C:\WINNT\system32\cmd.exe
HOMEDRIVE=C:
HOMEPATH=\Documents and Settings\Administrator
LOGONSERVER=\\SNOOPY
NUMBER_OF_PROCESSORS=1
OS=Windows_NT
Os2LibPath=C:\WINNT\system32\os2\dll;
Path=C:\WINNT\system32;C:\WINNT;C:\WINNT\System32\Wbem
PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH
PROCESSOR_ARCHITECTURE=x86
PROCESSOR_IDENTIFIER=x86 Family 6 Model 5 Stepping 2, GenuineIntel
PROCESSOR_LEVEL=6
PROCESSOR_REVISION=0502
ProgramFiles=C:\Program Files
PROMPT=$P$G
SystemDrive=C:
SystemRoot=C:\WINNT
TEMP=C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp
TMP=C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp
USERDOMAIN=SNOOPY
USERNAME=Administrator
USERPROFILE=C:\Documents and Settings\Administrator
windir=C:\WINNT
User Environment:
TEMP=%USERPROFILE%\Local Settings\Temp
TMP=%USERPROFILE%\Local Settings\Temp
Volatile Environment:
LOGONSERVER=\\SNOOPY
APPDATA=C:\Documents and Settings\Administrator\Application Data

By the way, if you add a new variable via the command prompt, you will not see it when you try to read it via the script. You can read only the new values created via the same scripting type you used to create them. Although I've tested this only to a limited extent, it seems to be true. Try it for yourself; just open a command prompt, type Set DUDE=Dudeworks, and press Enter to set the new environment variable. Now, when you execute GetEnvVars.vbs, and you'll notice that it does not list that new variable. However, if you type SET at the command prompt, you will see it.

Rob Olson