about_PSModulePath

Article
10/14/2024

Short description

This article describes the purpose and usage of the $env:PSModulePath environment variable.

Long description

The $env:PSModulePath environment variable contains a list of folder locations. PowerShell recursively searches each folder for module (.psd1 or .psm1) files.

By default, the effective locations assigned to $env:PSModulePath are:

Modules installed in the CurrentUser scope are stored in $HOME\Documents\WindowsPowerShell\Modules.
Modules installed in the AllUsers scope are stored in $env:ProgramFiles\WindowsPowerShell\Modules.
Modules that ship with Windows PowerShell stored in $PSHOME\Modules, which is $env:SystemRoot\System32\WindowsPowerShell\1.0\Modules.

PowerShell PSModulePath construction

The value of $env:PSModulePath is constructed each time PowerShell starts. The value varies by version of PowerShell and how you launched it.

Windows PowerShell startup

Windows PowerShell uses the following logic to construct the PSModulePath at startup:

If PSModulePath doesn't exist, combine CurrentUser, AllUsers, and the $PSHOME modules paths
If PSModulePath does exist:
- If PSModulePath contains $PSHOME modules path:
  - AllUsers modules path is inserted before $PSHOME modules path
- else:
  - Just use PSModulePath as defined since the user deliberately removed the $PSHOME location

The CurrentUser module path is prefixed only if the User scope $env:PSModulePath doesn't exist. Otherwise, the User scope $env:PSModulePath is used as defined.

Module search behavior

PowerShell recursively searches each folder in the PSModulePath for module (.psd1 or .psm1) files. This search pattern allows multiple versions of the same module to be installed in different folders. For example:

    Directory: C:\Program Files\WindowsPowerShell\Modules\PowerShellGet

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----           8/14/2020  5:56 PM                1.0.0.1
d----           9/13/2019  3:53 PM                2.1.2

By default, PowerShell loads the highest version number of a module when multiple versions are found. To load a specific version, use Import-Module with the FullyQualifiedName parameter. For more information, see Import-Module.

Modifying PSModulePath

For most situations, you should be installing modules in the default module locations. However, you might need to change the value of the PSModulePath environment variable.

For example, to temporarily add the C:\Program Files\Fabrikam\Modules directory to $env:PSModulePath for the current session, type:

$Env:PSModulePath = $Env:PSModulePath+";C:\Program Files\Fabrikam\Modules"

To change the value of PSModulePath in every session, edit the registry key storing the PSModulePath values. The PSModulePath values are stored in the registry as unexpanded strings. To avoid permanently saving the PSModulePath values as expanded strings, use the GetValue() method on the subkey and edit the value directly.

The following example adds the C:\Program Files\Fabrikam\Modules path to the value of the PSModulePath environment variable without expanding the unexpanded strings.

$key = (Get-Item 'HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Environment')
$path = $key.GetValue('PSModulePath','','DoNotExpandEnvironmentNames')
$path += ';%ProgramFiles%\Fabrikam\Modules'
$key.SetValue('PSModulePath',$path,[Microsoft.Win32.RegistryValueKind]::ExpandString)

To add a path to the user setting, use the following code:

$key = (Get-Item 'HKCU:\Environment')
$path = $key.GetValue('PSModulePath','','DoNotExpandEnvironmentNames')
$path += ';%ProgramFiles%\Fabrikam\Modules'
$key.SetValue('PSModulePath',$path,[Microsoft.Win32.RegistryValueKind]::ExpandString)

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