about_Environment_Variables

Artikkeli
09/05/2024

Short description

Describes how to access and manage environment variables in PowerShell.

Environment variables store data that's used by the operating system and other programs. PowerShell creates the following environment variables:

PSExecutionPolicyPreference
PSModulePath
PSModuleAnalysisCachePath
PSDisableModuleAnalysisCacheCleanup

For full descriptions of these variables, see the PowerShell environment variables of this article.

Long description

PowerShell can access and manage environment variables in any of the supported operating system platforms. The PowerShell environment provider lets you get, add, change, clear, and delete environment variables in the current console.

Environment variables, unlike other types of variables in PowerShell, are always stored as strings. Also unlike other variables, they're inherited by child processes, such as local background jobs and the sessions in which module members run. This makes environment variables well suited to storing values that are needed in both parent and child processes.

On Windows, environment variables can be defined in three scopes:

Machine (or System) scope
User scope
Process scope

The Process scope contains the environment variables available in the current process, or PowerShell session. This list of variables is inherited from the parent process and is constructed from the variables in the Machine and User scopes.

When you change environment variables in PowerShell, the change affects only the current session. This behavior resembles the behavior of the set command in the Windows Command Shell and the setenv command in UNIX-based environments. To change values in the Machine or User scopes, you must use the methods of the System.Environment class.

To make changes to Machine-scoped variables, you must also have permission. If you try to change a value without sufficient permission, the command fails and PowerShell displays an error.

PowerShell provides several different methods for using and managing environment variables.

The variable syntax
The Environment provider and Item cmdlets
The .NET System.Environment class

Use the variable syntax

You can display and change the values of environment variables with the following syntax:

$Env:<variable-name>

For example, to display the value of the WINDIR environment variable:

$Env:windir

C:\Windows

In this syntax, the dollar sign ($) indicates a variable, and the drive name (Env:) indicates an environment variable followed by the variable name (windir).

You can create and update the value of environment variables with the following syntax:

$Env:<variable-name> = "<new-value>"

For example, to create the Foo environment variable:

$Env:Foo = 'An example'

Because environment variables are always strings, you can use them like any other variable containing a string. For example:

"The 'Foo' environment variable is set to: $Env:Foo"
$Env:Foo += '!'
$Env:Foo

The 'Foo' environment variable is set to: An example

An example!

In PowerShell, an environment variable can't be set to an empty string. Setting an environment variable to $null or an empty string removes it from the current session. For example:

$Env:Foo = ''
$Env:Foo | Get-Member -MemberType Properties

Get-Member : You must specify an object for the Get-Member cmdlet.
At line:1 char:12
+ $env:foo | Get-Member
+            ~~~~~~~~~~
    + CategoryInfo          : CloseError: (:) [Get-Member], InvalidOperationException
    + FullyQualifiedErrorId : NoObjectInGetMember,Microsoft.PowerShell.Commands.GetMemberCommand

Get-Member returned an error because the environment variable was removed. You can see that it doesn't return an error when you use it on an empty string:

'' | Get-Member -MemberType Properties

   TypeName: System.String

Name   MemberType Definition
----   ---------- ----------
Length Property   int Length {get;}

For more information about variables in PowerShell, see about_Variables.

Use the Environment provider and Item cmdlets

PowerShell's Environment provider gives you an interface for interacting with environment variables in a format that resembles a file system drive. It lets you get, add, change, clear, and delete environment variables and values in PowerShell.

For example, to create the Foo environment variable with a value of Bar:

New-Item -Path Env:\Foo -Value 'Bar'

Name                           Value
----                           -----
Foo                            Bar

You can also copy the environment variable with Copy-Item, set the value of an environment variable with Set-Item, list environment variables with Get-Item, and delete the environment variable with Remove-Item.

Copy-Item -Path Env:\Foo -Destination Env:\Foo2 -PassThru
Set-Item -Path Env:\Foo2 -Value 'BAR'
Get-Item -Path Env:\Foo*
Remove-Item -Path Env:\Foo* -Verbose

Name                           Value
----                           -----
Foo2                           Bar

Name                           Value
----                           -----
Foo2                           BAR
Foo                            Bar

VERBOSE: Performing the operation "Remove Item" on target "Item: Foo2".
VERBOSE: Performing the operation "Remove Item" on target "Item: Foo".

Use the Get-ChildItem cmdlet to see a full list of environment variables:

Get-ChildItem Env:

For more information on using the Environment provider to manage environment variables, see about_Environment_Provider.

Use the System.Environment methods

The System.Environment class provides the GetEnvironmentVariable() and SetEnvironmentVariable() methods to get and modify environment variables.

The following example creates a new environment variable, Foo, with a value of Bar and then returns its value.

[Environment]::SetEnvironmentVariable('Foo','Bar')
[Environment]::GetEnvironmentVariable('Foo')

Bar

You can remove an environment variable with the SetEnvironmentVariable() method by specifying an empty string for the variable's value. For example, to remove the Foo environment variable:

[Environment]::SetEnvironmentVariable('Foo','')
[Environment]::GetEnvironmentVariable('Foo')

For more information about the methods of the System.Environment class, see Environment Methods.

Create persistent environment variables in Windows

On Windows, there are three methods for making a persistent change to an environment variable:

Set them in your profile
Using the SetEnvironmentVariable() method
Use the System Control Panel

Set environment variables in your profile

Any environment variable you add or change in your PowerShell profile is available in any session that loads your profile. This method works for any version of PowerShell on any supported platform.

For example, to create the CompanyUri environment variable and update the Path environment variable to include the C:\Tools folder, add the following lines to your PowerShell profile:

$Env:CompanyUri = 'https://internal.contoso.com'
$Env:Path += ';C:\Tools'

You can get the path to your PowerShell profile with the $PROFILE automatic variable. For more information on profiles, see about_Profiles.

Set environment variables with SetEnvironmentVariable()

On Windows, you can specify a scope for the SetEnvironmentVariable() method as the third parameter to set the environment variable in that scope. The machine and user scopes both persist outside of the current process, allowing you to save a new or changed environment variable.

For example, to save a new environment variable Foo with the value Barto the machine scope:

[Environment]::SetEnvironmentVariable('Foo', 'Bar', 'Machine')

You can delete an environment variable from the user or machine scope by setting the variable's value to an empty string.

[Environment]::SetEnvironmentVariable('Foo', '', 'Machine')

Set environment variables in the System Control Panel

In the System Control Panel, you can add or edit existing environment variables in the User and System (Machine) scopes. Windows writes these values to the Registry so that they persist across sessions and system restarts.

To make a persistent change to an environment variable on Windows using the System Control Panel:

Open the System Control Panel.
Select System.
Select Advanced System Settings.
Go to the Advanced tab.
Select Environment Variables....
Make your changes.

PowerShell environment variables

PowerShell features can use environment variables to store user preferences. These variables work like preference variables, but they're inherited by child sessions of the sessions in which they're created. For more information about preference variables, see about_Preference_Variables.

The environment variables that store preferences include:

PSExecutionPolicyPreference

Stores the execution policy set for the current session. This environment variable exists only when you set an execution policy for a single session. You can do this in two different ways.
- Start a session from the command line using the ExecutionPolicy parameter to set the execution policy for the session.
- Use the Set-ExecutionPolicy cmdlet. Use the Scope parameter with a value of Process.
- Manually set the environment variable. Changing the value of this variable changes the execution policy of the current process.
This information only applies to the Windows platform. For more information, see about_Execution_Policies.
PSModulePath

The $env:PSModulePath environment variable contains a list of folder locations that are searched to find modules and resources.

By default, the effective locations assigned to $env:PSModulePath are:
- System-wide locations: These folders contain modules that ship with PowerShell. The modules are store in the $PSHOME\Modules location. Also, This is the location where the Windows management modules are installed.
- User-installed modules: These are modules installed by the user. 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.
  - On Windows, the location of the user-specific CurrentUser scope is the $HOME\Documents\PowerShell\Modules folder. The location of the AllUsers scope is $env:ProgramFiles\PowerShell\Modules.
In addition, setup programs that install modules in other directories, such as the Program Files directory, can append their locations to the value of $env:PSModulePath.

For more information, see about_PSModulePath.
PSModuleAnalysisCachePath

PowerShell provides control over the file that's used to cache data about modules and their cmdlets. The cache is read at startup while searching for a command and is written on a background thread sometime after a module is imported.

The default location of the cache is:
- $env:LOCALAPPDATA\Microsoft\Windows\PowerShell
The default filename for the cache is ModuleAnalysisCache.

Note

If command discovery isn't working correctly, for example IntelliSense shows commands that don't exist, you can delete the cache file. The cache is recreated the next time you start PowerShell.

To change the default location of the cache, set the environment variable before starting PowerShell. The value should name a full path (including filename) that PowerShell has permission to create and write files.

Changes to this environment variable only affect child processes. See the previous sections for information about creating persistent environment variables.

To disable the file cache, set this value to an invalid location, for example:
```
# `NUL` here is a special device on Windows that can't be written to
$env:PSModuleAnalysisCachePath = 'NUL'
```
This sets the path to the NUL device. PowerShell can't write to the path but no error is returned. You can see the errors reported using a tracer:
```
Trace-Command -PSHost -Name Modules -Expression {
  Import-Module Microsoft.PowerShell.Management -Force
}
```
PSDisableModuleAnalysisCacheCleanup

When writing out the module analysis cache, PowerShell checks for modules that no longer exist to avoid an unnecessarily large cache. Sometimes these checks aren't desirable, in which case you can turn them off by setting this environment variable value to 1.

Setting this environment variable takes effect for subsequent cleanup events in the current process. To ensure that cleanup is disabled at startup, you must set the environment variable before starting PowerShell. See the previous sections for information about creating persistent environment variables.

Other environment variables used by PowerShell

Path information

PATH

The $env:PATH environment variable contains a list of folder locations that the operating system searches for executable files. On Windows, the list of folder locations is separated by the semi-colon (;) character.
PATHEXT

The $env:PATHEXT variable contains a list of file extensions that Windows considers to be executable files. When a script file with one of the listed extensions is executed from PowerShell, the script runs in the current console or terminal session. If the file extension isn't listed, the script runs in a new console session.

To ensure that scripts for another scripting language run in the current console session, add the file extension used by the scripting language. For example, to run Python scripts in the current console, add the .py extension to the environment variable. For Windows to support the .py extension as an executable file you must register the file extension using the ftype and assoc commands of the CMD command shell. PowerShell has no direct method to register the file handler. For more information, see the documentation for the ftype command.

PowerShell scripts always start in the current console session. You don't need to add the .PS1 extension.

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