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ABOUT ENVIRONMENT VARIABLES
SHORT DESCRIPTION
Describes how to access Windows environment variables in PowerShell.
LONG DESCRIPTION
Environment variables store information about the operating system
environment. This information includes details such as the operating system
path, the number of processors used by the operating system, and the
location of temporary folders.
The environment variables store data that is used by the operating system
and other programs. For example, the WINDIR environment variable contains
the location of the Windows installation directory. Programs can query the
value of this variable to determine where Windows operating system files
are located.
PowerShell can access and manage environment variables in any of the
supported operating system platforms. The PowerShell environment provider
simplifies this process by making it easy to view and change environment
variables.
Environment variables, unlike other types of variables in PowerShell, are
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.
Changing environment variables
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, must also have permission. If
you try to change a value without sufficient permission, the command fails
and PowerShell displays an error.
You can change the values of variables without using a cmdlet using the
following syntax:
$Env:<variable-name> = "<new-value>"
For example, to append ;c:\temp to the value of the Path environment
variable, use the following syntax:
$Env:Path += ";c:\temp"
You can also use the Item cmdlets, such as Set-Item, Remove-Item, and
Copy-Item to change the values of environment variables. For example, to
use the Set-Item cmdlet to append ;c:\temp to the value of the Path
environment variable, use the following syntax:
Set-Item -Path Env:Path -Value ($Env:Path + ";C:\Temp")
In this command, the value is enclosed in parentheses so that it is
interpreted as a unit.
Environment variables that store preferences
PowerShell features can use environment variables to store user
preferences. These variables work like preference variables, but they are
inherited by child sessions of the sessions in which they are 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".
For more information, see about_Execution_Policies.
- PSModuleAnalysisCachePath
PowerShell provides control over the file that is 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.
Default location of the cache is:
- $env:LOCALAPPDATA\Microsoft\Windows\PowerShell
The default filename for the cache is ModuleAnalysisCache. To change
the default location of the cache, set the environment variable before
starting PowerShell. Changes to this environment variable only affect
child processes. The value should name a full path (including filename)
that PowerShell has permission to create and write files.
[!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 disable the file cache, set this value to an invalid location, for
example:
# `NUL` here is a special device on Windows that cannot 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 are not desirable, in which case you can turn
them off by setting this environment variable value to 1.
Setting this environment variable takes effect immediately in the
current process.
- 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.
Managing environment variables
PowerShell provides several different methods for managing environment
variables.
- The Environment provider drive
- The Item cmdlets
- The .NET SYSTEM.ENVIRONMENT class
- On Windows, the System Control Panel
Using the Environment provider
Each environment variable is represented by an instance of the
SYSTEM.COLLECTIONS.DICTIONARYENTRY class. In each DICTIONARYENTRY object,
the name of the environment variable is the dictionary key. The value of
the variable is the dictionary value.
To display the properties and methods of the object that represents an
environment variable in PowerShell, use the Get-Member cmdlet. For example,
to display the methods and properties of all the objects in the Env: drive,
type:
Get-Item -Path Env:* | Get-Member
The PowerShell Environment provider lets you access environment variables
in a PowerShell drive (the Env: drive). This drive looks much like a file
system drive. To go to the Env: drive, type:
Set-Location Env:
Use the Content cmdlets to get or set the values of an environment
variable.
PS Env:\> Set-Content -Path Test -Value 'Test value'
PS Env:\> Get-Content -Path Test
Test value
You can view the environment variables in the Env: drive from any other
PowerShell drive, and you can go into the Env: drive to view and change the
environment variables.
Using Item cmdlets
When you refer to an environment variable, type the Env: drive name
followed by the name of the variable. For example, to display the value of
the COMPUTERNAME environment variable, type:
Get-ChildItem Env:Computername
To display the values of all the environment variables, type:
Get-ChildItem Env:
Because environment variables do not have child items, the output of
Get-Item and Get-ChildItem is the same.
By default, PowerShell displays the environment variables in the order in
which it retrieves them. To sort the list of environment variables by
variable name, pipe the output of a Get-ChildItem command to the
Sort-Object cmdlet. For example, from any PowerShell drive, type:
Get-ChildItem Env: | Sort Name
You can also go into the Env: drive by using the Set-Location cmdlet:
Set-Location Env:
When you are in the Env: drive, you can omit the Env: drive name from the
path. For example, to display all the environment variables, type:
PS Env:\> Get-ChildItem
To display the value of the COMPUTERNAME variable from within the Env:
drive, type:
PS Env:\> Get-ChildItem ComputerName
Using variable syntax
You can also display and change the values of environment variables without
using a cmdlet by using the expression parser in PowerShell. To display the
value of an environment variable, use the following syntax:
$Env:<variable-name>
For example, to display the value of the WINDIR environment variable, type
the following command at the PowerShell command prompt:
$Env:windir
In this syntax, the dollar sign ($) indicates a variable, and the drive
name indicates an environment variable.
Saving changes to environment variables
To make a persistent change to an environment variable on Windows, use the
System Control Panel. Select ADVANCED SYSTEM SETTINGS. On the ADVANCED tab,
click ENVIRONMENT VARIABLE.... 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.
Alternately, you can add or change environment variables in your PowerShell
profile. This method works for any version of PowerShell on any supported
platform.
Using System.Environment methods
The SYSTEM.ENVIRONMENT class provides GETENVIRONMENTVARIABLE and
SETENVIRONMENTVARIABLE methods that allow you to specify the scope of the
variable.
The following example uses the GETENVIRONMENTVARIABLE method to get the
machine setting of PSModulePath and the SETENVIRONMENTVARIABLE method to
add the C:\Program Files\Fabrikam\Modules path to the value.
$path = [Environment]::GetEnvironmentVariable('PSModulePath', 'Machine')
$newpath = $path + ';C:\Program Files\Fabrikam\Modules'
[Environment]::SetEnvironmentVariable("PSModulePath", $newpath, 'Machine')
For more information about the methods of the SYSTEM.ENVIRONMENT class, see
Environment Methods.
SEE ALSO
- Environment (provider)
- about_Modules