Environment variables are not often seen directly when using Windows. However there are cases, especially when using the command line, that setting and updating environment variables is a necessity. In this series we talk about the various approaches we can take to set them. In this article we look at how to interface with environment variables using the Command Prompt and Windows PowerShell. We also note where in the registry the environment variables are set, if you needed to access them in such a fashion.

You can use environment variables in the values of other environment variables. It is then helpful to be able to see what environment variables are set already. This is how you do it:

Command Prompt

List all environment variables

Command Prompt - C:\>

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set

Output

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ALLUSERSPROFILE=C:\ProgramData
APPDATA=C:\Users\user\AppData\Roaming
.
.
.
windir=C:\Windows

Print a particular environment variable:

Command Prompt - C:\>

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echo %ProgramFiles%

Output

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C:\Program Files

Windows PowerShell

List all environment variables

Windows PowerShell - PS C:\>

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Get-ChildItem Env:

Output

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Name                           Value
----                           -----
ALLUSERSPROFILE                C:\ProgramData
APPDATA                        C:\Users\user\AppData\Roaming
.
.
.
windir                         C:\Windows

Print a particular environment variable:

Windows PowerShell - PS C:\>

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echo $Env:ProgramFiles

Output

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C:\Program Files

Set Environment Variables

To set persistent environment variables at the command line, we will use setx.exe. It became part of Windows as of Vista/Windows Server 2008. Prior to that, it was part of the Windows Resource Kit. If you need the Windows Resource Kit, see Resources at the bottom of the page.

setx.exe does not set the environment variable in the current command prompt, but it will be available in subsequent command prompts.

User Variables

Command Prompt - C:\>

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setx EC2_CERT "%USERPROFILE%\aws\cert.pem"

Open a new command prompt.

Command Prompt - C:\>

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echo %EC2_CERT%

Output

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C:\Users\user\aws\cert.pem

System Variables

To edit the system variables, you’ll need an administrative command prompt. See HowTo: Open an Administrator Command Prompt in Windows to see how.

Command Prompt - C:\>

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setx EC2_HOME "%APPDATA%\aws\ec2-api-tools" /M

Registry

Warning This method is recommended for experienced users only.

The location of the user variables in the registry is: HKEY_CURRENT_USER\Environment. The location of the system variables in the registry is: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment.

When setting environment variables through the registry, they will not recognized immediately. One option is to log out and back in again. However, we can avoid logging out if we send a WM_SETTINGCHANGE message, which is just another line when doing this programatically, however if doing this on the command line it is not as straightforward.

One way is to get this message issued is to open the environment variables in the GUI, like we do in HowTo: Set an Environment Variable in Windows - GUI; we do not need to change anything, just open the Environment Variables window where we can see the environment variables, then hit OK.

Another way to get the message issued is to use setx, this allows everything to be done on the command line, however requires setting at least one environment variable with setx.

Printing Environment Variables

With Windows XP, the reg tool allows for accessing the registry from the command line. We can use this to look at the environment variables. This will work the same way in the command prompt or in powershell. This technique will also show the unexpanded environment variables, unlike the approaches shown for the command prompt and for powershell.

First we’ll show the user variables:

Command Prompt - C:\>

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reg query HKEY_CURRENT_USER\Environment

Output

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HKEY_CURRENT_USER\Environment
    TEMP    REG_EXPAND_SZ    %USERPROFILE%\AppData\Local\Temp
    TMP    REG_EXPAND_SZ    %USERPROFILE%\AppData\Local\Temp

We can show a specific environment variable by adding /v then the name, in this case we’ll do TEMP:

Command Prompt - C:\>

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reg query HKEY_CURRENT_USER\Environment /v TEMP

Output

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HKEY_CURRENT_USER\Environment
    TEMP    REG_EXPAND_SZ    %USERPROFILE%\AppData\Local\Temp

Now we’ll list the system environment variables:

Command Prompt - C:\>

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reg query "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment"

Output

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HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment
    ComSpec    REG_EXPAND_SZ    %SystemRoot%\system32\cmd.exe
    FP_NO_HOST_CHECK    REG_SZ    NO
    NUMBER_OF_PROCESSORS    REG_SZ    8
    OS    REG_SZ    Windows_NT
    Path    REG_EXPAND_SZ    C:\ProgramData\Oracle\Java\javapath;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\;%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;%SYSTEMROOT%\System32\WindowsPowerShell\v1.0\
    PATHEXT    REG_SZ    .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC
    PROCESSOR_ARCHITECTURE    REG_SZ    AMD64
    PROCESSOR_IDENTIFIER    REG_SZ    Intel64 Family 6 Model 60 Stepping 3, GenuineIntel
    PROCESSOR_LEVEL    REG_SZ    6
    PROCESSOR_REVISION    REG_SZ    3c03
    PSModulePath    REG_EXPAND_SZ    %SystemRoot%\system32\WindowsPowerShell\v1.0\Modules\;C:\Program Files\Intel\
    TEMP    REG_EXPAND_SZ    %SystemRoot%\TEMP
    TMP    REG_EXPAND_SZ    %SystemRoot%\TEMP
    USERNAME    REG_SZ    SYSTEM
    windir    REG_EXPAND_SZ    %SystemRoot%

And same as with the user variables we can query a specific variable.

Command Prompt - C:\>

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reg query "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment" /v PATH

Output

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HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment
    PATH    REG_EXPAND_SZ    C:\ProgramData\Oracle\Java\javapath;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\;%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;%SYSTEMROOT%\System32\WindowsPowerShell\v1.0\

Unsetting a Variable

When setting environment variables on the command line, setx should be used because then the environment variables will be propagated appropriately. However one notable thing setx doesn’t do is unset environment variables. The reg tool can take care of that, however another setx command should be run afterwards to propagate the environment variables.

The layout for deleting a user variable is: reg delete HKEY_CURRENT_USER\Environment /v variable_name /f. If /f had been left off, we would have been prompted: Delete the registry value EXAMPLE (Yes/No)?. For this example we’ll delete the user variable USER_EXAMPLE:

Command Prompt - C:\>

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reg delete HKEY_CURRENT_USER\Environment /v USER_EXAMPLE /f

Output

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The operation completed successfully.

Deleting a system variable requires administrator privileges. See HowTo: Open an Administrator Command Prompt in Windows to see how to do this.

The layout for deleting a system variable is: reg delete "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment" /v variable_name /f. For this example we’ll delete the system variable SYSTEM_EXAMPLE:

Command Prompt - C:\>

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reg delete "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment" /v SYSTEM_EXAMPLE /f

If this was run as a normal user you’ll get:

Output

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ERROR: Access is denied.

But run in an administrator shell will give us:

Output

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The operation completed successfully.

Finally we’ll have to run a setx command to propagate the environment variables. If there were other variables to set, we could just do that now. However if we were just interested in unsetting variables, we will need to have one variable left behind. In this case we’ll set a user variable named throwaway with a value of trash

Command Prompt - C:\>

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setx throwaway trash

Output

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SUCCESS: Specified value was saved.

Resources

Windows Server 2003 Resource Kit Tools will also work with Windows XP and Windows XP SP1; use Windows XP Service Pack 2 Support Tools with Windows XP SP2. Neither download is supported on 64-bit version.

Parts in this series

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