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I don't understand this. So currently my system environment variable named "PSModulePath" looks like this:

%ProgramFiles%\WindowsPowerShell\Modules;%SystemRoot%\system32\WindowsPowerShell\v1.0\Modules

Now observe the following PowerShell script:

$envarname = "PSModulePath"
$envar = (get-item env:$envarname).Value
[Environment]::SetEnvironmentVariable($envarname, $envar + ";C:\Expedited", "Machine")

All it should be doing is adding the path "C:\Expedited" to the PSModulesPath environment variable, right? Well, after running this script as administrator, the PSModulePath environment variable changes into this:

C:\Users\Username\Documents\WindowsPowerShell\Modules;C:\Program Files\WindowsPowerShell\Modules;C:\Windows\system32\WindowsPowerShell\v1.0\Modules;C:\Expedited

Notice how:

  1. There were originally two paths, each of which contained percentage signs (variables) in the original, but afterward they all changed directly into hard-coded paths.
  2. The "C:\Users\Username\Documents\WindowsPowerShell\Modules" path sprung out of nowhere (it wasn't in the original!)

I don't have any idea why either of these two things happened. When adding a path to this variable, I would like to keep it as close to the original as possible, not make all these other changes. Is there any way to preserve the percentage signs that were lost? How do I edit this environment variable correctly from within PowerShell?

  • "C:\Users\Username\Documents\WindowsPowerShell\Modules" - This would only exist in the user's PATH variable. It appears you are modifying the user's PATH variable instead of the system's PATH variable hence the difference. This question has an answer that explains the differences. – Ramhound Jul 16 '18 at 19:55
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    @PimpJuiceIT, just open System Properties\Advanced\Environment Variables and take a look in there yourself. If you use the actual UI, or even check the corresponding registry entry, you can see the percentage signs in the text string. The problem is that I cannot get the string with the percentage signs using PowerShell for some reason; they always get converted to hard-coded paths and I don't know why. – jippyjoe4 Jul 17 '18 at 17:06
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PowerShell - Get OS Environmental Variables without Expanding

You can use the Get-Item cmdlet with the -path parameter and then pass that the path of the registry key containing the PSModulePath environmental variable.

You can then use the RegistryKey.GetValue Method along with DoNotExpandEnvironmentNames to get the string value of the PSModulePath environmental variable without expanding it.


PowerShell

$envarname = "PSModulePath"
$regkey    = Get-Item -Path "HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Environment"
$envar     = $regkey.GetValue($envarname, "", "DoNotExpandEnvironmentNames")
ECHO $envar

Note: You will want to be sure you run this from administrator elevated PowerShell command prompt or ISE screen for it to work correctly.

enter image description here


Further Resources

  • jippyjoe4 - This explains why and gives a way to get the OS Environmental Variables without expanding other environmental variables within their values to retain the percent sign. In case it's not clear as to why explicitly though, it's because the other variables within that variable are being expanded so this is a way to prevent with simple to follow code that's not very complex. – Pimp Juice IT Jul 17 '18 at 23:17
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You are doing extra steps that are not really needed for your end goal. Just use the default as shown in the MS guidance.

https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_environment_variables?view=powershell-6

So, based on the above article, you should only need that last example, or just one line, by using the built-in default / automatic environment variables.

[System.Environment]::SetEnvironmentVariable("PSModulePath", $Env:PSModulePath + ";C:\Expedited","Machine")
  • You're right, that method is simpler than my code, but it still results in the same two undesired effects I listed in my original question. Do you have an explanation for those? – jippyjoe4 Jul 17 '18 at 0:55

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