Environment variables are one of those features of Windows that have been around for a long time. As part of the operating system, all scripting languages have been able to read both user and system-level environment variables, but none have made it easier to work with them than PowerShell.

Adam Bertram

Adam Bertram is a 20-year IT veteran, Microsoft MVP, blogger, and trainer. Adam is the founder of the e-learning tech screencast platform TechSnips. Catch up on Adam’s articles at adamtheautomator.com, or follow TechSnips on Twitter at @techsnips_io.

In this article, I'll go over a few different ways a scripter can work with environment variables in PowerShell.

Environment variables are exposed with a PowerShell drive known as "$env:". It's possible to browse through all of the environment variables by typing $env: at the console and hitting the tab key. This will allow you to see the names of each environment variable in alphabetical order.

The $env: drive is the recommended place to refer to any environment variables with PowerShell. However, it's possible also to read the variables via .NET in PowerShell by using the GetEnvironmentVariable static method on the Environment class. This is essentially the same task.

This will output the same CLIENT1 as seen above.

As you can see, reading environment variables is easy. How do we set them? There are a few ways to do this. Each method is a little different and, more importantly, makes the environment variable active during various times.

The first way to set an environment variable is to change the $env: drive's variable directly.

Assigning environment variable via PS Drive

Assigning environment variable via PS Drive

This method works but has limitations. The main one being that the variable is only active in the current user session; it is not permanent. This means that as soon as the console is closed, this new assignment will be removed and will revert to what it originally was. This method can be used to change existing environment variables or create new ones. It also allows you to immediately refer to the environment variable (as you can see above).

What if you need to create permanent environment variables? We'll need to go into .NET to do this. To create permanent environment variables that last through a single session, we'll need to use the SetEnvironmentVariable method. This method has three arguments: the variable name, value, and type (System or User).

Setting an environment variable

Setting an environment variable

At first, you may think that nothing happened. As you can see above, I supposedly set the variable in the user session, but $env:test does not find it. This is a downside of this method. This variable does not show up until the session has been restarted.

Test environment variable after restarting the session

Test environment variable after restarting the session

Just because it didn't show up in the $env drive doesn't mean it wasn't there. You could always use the GetEnvironmentVariable() method to find it without having to start a new session.

The same approach can be applied to creating and changing system environment variables as well. However, instead of specifying "User" as the argument for Get and SetEnvironmentVariable, you would use "System" instead.

You'll find that even though using the PowerShell drive to refer to environment variables is handy, it's not real-time nor is it permanent. In my experience, I've always chosen to use the .NET methods to control environment variables. Using these methods, you're able to set environment variables permanently and retrieve them without session restarts. There have also been times when system environment variables simply don't show up in the $env drive, and you'll be forced to use the .NET methods anyway.

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3 Comments
  1. Luc Fullenwarth 2 years ago

    You can also enumerate them with Get-ChildItem -Path Env:

    Good post!
    Thanks Adam!

    1+

  2. Erik 1 year ago

    In testing this out,  I found that [Environment]::GetEnvironmentVariable("Comspec", "System"yielded the following error:

    Cannot convert argument "target", with value: "System", for "GetEnvironmentVariable" to type
    "System.EnvironmentVariableTarget"

    [Environment]::GetEnvironmentVariable("Comspec", "Machine") gives the correct result.

    [Environment]::GetEnvironmentVariable("Comspec","Machine")
    C:\Windows\system32\cmd.exe

    0

  3. Paul 1 year ago

    How about retrieving environment values from a previously running process? How can I get them?

    0

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