The Windows System control panel for editing env vars.
Xah Lee, 2009-10-03, 2010-06-18
This document is a basic tutorial about Windows's Environment Variables. The code here is tested on Windows Vista.
Environment variables are system-wide global variables. They are somewhat like config parameters, and is used by processes. For example, apps need to know the path of your Windows kernal, path to cmd.exe, path of your home dir, paths to search for shell programs, etc.
To view and set your env var, go to Control Panel, then click the “System” icon, then click the “Advanced system settings” link, then “Advanced” tab, Environment Variables button.
The Windows System control panel for editing env vars.
You can launch the app directly in cmd.exe or PowerShell by typing the following (Windows Vista):
c:/Windows/System32/SystemPropertiesAdvanced.exe
Env var names are not case sensitive. So, “PATH”, “Path”, “path” are treated the same.
Here's example of env var values as it exists on my system.
Name Value ---- ----- ALLUSERSPROFILE C:\ProgramData APPDATA C:\Users\xah\AppData\Roaming CLASSPATH .;C:\Program Files (x86)\Java\jre6\lib\ext\QTJava.zip CommonProgramFiles C:\Program Files\Common Files CommonProgramFiles(x86) C:\Program Files (x86)\Common Files COMPUTERNAME XAH-PC ComSpec C:\Windows\system32\cmd.exe DFSTRACINGON FALSE ERGOEMACS_KEYBOARD_LAYOUT dv FP_NO_HOST_CHECK NO HOME c:/Users/xah HOMEDRIVE C: HOMEPATH \Users\xah LOCALAPPDATA C:\Users\xah\AppData\Local LOGONSERVER \\XAH-PC NUMBER_OF_PROCESSORS 4 OnlineServices Online Services OS Windows_NT Path C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Program Files (x8... PATHEXT .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC;.PSC1 PCBRAND Pavilion Platform HPD PROCESSOR_ARCHITECTURE AMD64 PROCESSOR_IDENTIFIER AMD64 Family 16 Model 2 Stepping 3, AuthenticAMD PROCESSOR_LEVEL 16 PROCESSOR_REVISION 0203 ProgramData C:\ProgramData ProgramFiles C:\Program Files ProgramFiles(x86) C:\Program Files (x86) PSMODULEPATH C:\Users\xah\Documents\WindowsPowerShell\Modules;C:\Windows\system32\Windows... PUBLIC C:\Users\Public PYTHONDOCS C:\Users\xah\na_xruti\python-2.6.2-docs-html QTJAVA C:\Program Files (x86)\Java\jre6\lib\ext\QTJava.zip SESSIONNAME Console SystemDrive C: SystemRoot C:\Windows TEMP C:\Users\xah\AppData\Local\Temp TMP C:\Users\xah\AppData\Local\Temp TRACE_FORMAT_SEARCH_PATH \\NTREL202.ntdev.corp.microsoft.com\34FB5F65-FFEB-4B61-BF0E-A6A76C450FAA\Tra... USERDOMAIN xah-PC USERNAME xah USERPROFILE C:\Users\xah windir C:\Windows
One of the most important env var is the PATH. Here's a sample value of path as set in my system (with line break added for easy reading):
C:\Windows\system32; C:\Windows; C:\Windows\System32\Wbem; C:\Program Files (x86)\Java\jdk1.6.0_14\bin; C:\hp\bin\Python; c:\Program Files (x86)\ATI Technologies\ATI.ACE\Core-Static; C:\Windows\system32\WindowsPowerShell\v1.0\; c:\Program Files (x86)\Microsoft SQL Server\100\Tools\Binn\; c:\Program Files (x86)\Microsoft SQL Server\100\DTS\Binn\; C:\Program Files (x86)\QuickTime\QTSystem\
A env var can be Local or System. Local means per session, temporary. System means permanent. System env vars are also grouped into User and Machine groups.
Local env var are created by a command shell (cmd.exe or PowerShell).
Local env var are also known as “Process env var”. They are per session env vars. They are temporary.
When you use “set” in cmd.exe to create set a variable, it creates a local env var. When you restart the shell, they are gone.
When programs are launched from the shell, they get all env vars including Process category env vars.
System env var are those stored in Windows Registry. They are permanent.
System env var can be created by a command line shell or programing language.
System env vars has 2 categories: User and Machine.
The “User” category env vars are things like home dir (HOME), temp dir (TEMP and or TMP).
In Registry, they are at:
HKEY_CURRENT_USER\Environment
The “Machine” category env vars are any other, usually related to your machine or more general info. For example: OS kernal path (WINDIR), processor info (PROCESSOR_ARCHITECTURE, NUMBER_OF_PROCESSORS, etc), application paths (PATH), executable file name extensions (PATHEXT), OS type (OS), current user name (USERNAME), etc.
In Registry, they are at:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment
For a intro of Registry see: Microsoft Windows Registry Tutorial.
Note that you can set any new env vars in any category. Programs have access to all your env vars, but which ones are meaningful to the program is up to the program.
To show a value of a env var, type “echo %‹env var name›%”. For example, to show the “path” env var, do:
echo %path%
To see all your env vars, type:
set
To see all env vars starting with “p”, type:
set p
To set env var for the current session, use “set ‹var name›=‹value›”. WARNING: make sure there's no space around the equal sign. Example:
set xx=5 echo %xx% REM prints 5. (REM is a comment syntax, everything after it is ignored.)
REM prepending a path to the “path” env var set PATH="C:\Program Files (x86)\ErgoEmacs;%PATH%"
To set env var permanently, use “setx” command. The “setx” command is part of cmd.exe in Windows Vista. Here's a example:
REM example of setting HOME env var setx HOME "C:\Users\mary"
REM example of adding a path setx PATH "C:\Program Files (x86)\ErgoEmacs;%PATH%"
For detail, type “setx /?”.
Note: when you set a env var using “setx”, it is set in the registry, however, they are not known in the current session. Restart the shell if you want them to be available.
Using PowerShell to Manage Environment Variables.
technet.microsoft.com Command shell overview
msdn.microsoft.com Environment Methods