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 that are searched to find modules and resources. PowerShell recursively searches each folder for module (.psd1 or .psm1) files.

Install-Module has a Scope parameter that allows you to specify whether the module is installed for the current user or for all users. For more information, see Install-Module.

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

  • System-wide locations: These folders contain modules that ship with PowerShell. These modules are stored in the $PSHOME\Modules folder.

    • On Windows, modules installed in the AllUsers scope are stored in $env:ProgramFiles\WindowsPowerShell\Modules.
    • On non-Windows systems, modules installed in the AllUsers scope are stored in /usr/local/share/powershell/Modules.
  • User-installed modules: On Windows, modules installed in the CurrentUser scope are typically stored in the $HOME\Documents\WindowsPowerShell\Modules folder. The specific location of the Documents folder varies by version of Windows and when you use folder redirection. Also, Microsoft OneDrive can change the location of your Documents folder. You can verify the location of your Documents folder using the following command: [Environment]::GetFolderPath('MyDocuments').

    On non-Windows systems, modules installed in the CurrentUser scope are stored in the $HOME/.local/share/powershell/Modules folder.

  • Application specific modules: Setup programs can install modules in other directories, such as the Program Files folder on Windows. The installer package may or may not append the location to the $env:PSModulePath.

PowerShell PSModulePath construction

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

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.

PowerShell 7 startup

In Windows, for most environment variables, if the User-scoped variable exists, a new process uses that value only even if a Machine-scoped variable of the same name exists.

In PowerShell 7, PSModulePath is treated similar to how the Path environment variable is treated on Windows. On Windows, Path is treated differently from other environment variables. When a process is started, Windows combines the User-scoped Path with the Machine-scoped Path.

  • Retrieve the User-scoped PSModulePath
  • Compare to process inherited PSModulePath environment variable
    • If the same:
      • Append the AllUsers PSModulePath to the end following the semantics of the Path environment variable
      • The Windows System32 path comes from the machine defined PSModulePath so does not need to be added explicitly
    • If different, treat as though user explicitly modified it and don't append AllUsers PSModulePath
  • Prefix with PS7 User, System, and $PSHOME paths in that order
    • If powershell.config.json contains a user scoped PSModulePath, use that instead of the default for the user
    • If powershell.config.json contains a system scoped PSModulePath, use that instead of the default for the system

Unix systems don't have a separation of User and System environment variables. PSModulePath is inherited and the PS7-specific paths are prefixed if not already defined.

Starting Windows PowerShell from PowerShell 7

For this discussion, Windows PowerShell means both powershell.exe and powershell_ise.exe.

The value of $env:PSModulePath is copied to WinPSModulePath with the following modifications:

  • Remove PS7 the User module path
  • Remove PS7 the System module path
  • Remove PS7 the $PSHOME module path

The PS7 paths are removed so that PS7 modules don't get loaded in Windows PowerShell. The WinPSModulePath value is used when starting Windows PowerShell.

Starting PowerShell 7 from Windows PowerShell

The PowerShell 7 startup continues as-is with the addition of inheriting paths that Windows PowerShell added. Since the PS7-specific paths are prefixed, there is no functional issue.

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      
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 may have a 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"

The semi-colon (;) in the command separates the new path from the path that precedes it in the list. On non-Windows platforms, the colon (:) separates the path locations in the environment variable.

Modifying PSModulePath in non-Windows

To change the value of PSModulePath for every session in a non-Windows environment, add the previous command to your PowerShell profile.

Modifying PSModulePath in Windows

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 un-expanded strings.

$key = (Get-Item 'HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager').OpenSubKey('Environment', $true)
$path = $key.GetValue('PSModulePath','','DoNotExpandEnvironmentNames')
$path += ';%ProgramFiles%\Fabrikam\Modules'

To add a path to the user setting, change the registry provider from HKLM:\ to HKCU:\.

$key = (Get-Item 'HKCU:\').OpenSubKey('Environment', $true)
$path = $key.GetValue('PSModulePath','','DoNotExpandEnvironmentNames')
$path += ';%ProgramFiles%\Fabrikam\Modules'

See also