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about_Variable_Provider

Provider name

Variable

Drives

Variable:

Capabilities

ShouldProcess

Short description

Provides access to the PowerShell variables and to their values.

Detailed description

The PowerShell Variable provider lets you get, add, change, clear, and delete PowerShell variables in the current console.

The PowerShell Variable provider supports the variables that PowerShell creates, including the automatic variables, the preference variables, and the variables that you create.

The Variable drive is a flat namespace that contains only the variable objects. The variables have no child items.

The Variable provider supports the following cmdlets, which are covered in this article.

PowerShell also includes a set of cmdlets designed especially to view and to change variables. When you use Variable cmdlets, you do not need to specify the Variable: drive in the name. This article does not cover working with Variable cmdlets.

Note

You can also use the PowerShell expression parser to create, view, and change the values of variables without using the cmdlets. When working with variables directly, use a dollar sign ($) to identify the name as a variable and the assignment operator (=)to establish and change its value. For example, $p = Get-Process creates the p variable and stores the results of a Get-Process command in it.

Types exposed by this provider

Variables can be one of several different types. Most variables will be instances of the PSVariable class. Other variables and their types are listed below.

  • The ? variable is an instance of the QuestionMarkVariable class.
  • The null variable is an instance of the NullVariable class.
  • The maximum count variables are instances of the SessionStateCapacityVariable class.
  • LocalVariable instances contain information about current execution, such as:
    • MyInvocation
    • PSCommandPath
    • PSScriptRoot
    • PSBoundParameters
    • args
    • input

The Variable provider exposes its data store in the Variable: drive. To work with variables, you can change your location to the Variable: drive (Set-Location Variable:), or you can work from any other PowerShell drive. To reference a variable from another location, use the drive name (Variable:) in the path.

Set-Location Variable:

To return to a file system drive, type the drive name. For example, type:

Set-Location C:

You can also work with the Variable provider from any other PowerShell drive. To reference a variable from another location, use the drive name Variable: in the path.

Note

PowerShell uses aliases to allow you a familiar way to work with provider paths. Commands such as dir and ls are now aliases for Get-ChildItem, cd is an alias for Set-Location. and pwd is an alias for Get-Location.

Displaying the value of variables

Get all variables in the current session

This command gets the list of all the variables and their values in the current session. You can use this command from any PowerShell drive.

Get-ChildItem -Path Variable:

Get a variable using its provider path

This command retrieves a variables value using its provider path prefixed by the dollar sign ($). This has the same effect as prefixing the variables name with the dollar sign ($).

$Variable:HOME

Get variables using wildcards

This command gets the variables with names that begin with "Max". You can use this command from any PowerShell drive.

Get-ChildItem -Path Variable:Max*

Get the value of the ? variable

This command uses the -LiteralPath parameter of Get-ChildItem to get the value of the ? variable from within the Variable: drive. The ? is a wildcard in paths, but Get-ChildItem does not attempt to resolve any wildcards in the values of the -LiteralPath parameter.

Get-ChildItem -LiteralPath ?

Get ReadOnly and Constant variables

This command gets the variables that have the values of ReadOnly or Constant for their Options property.

Get-ChildItem -Path Variable: |
    Where-Object {
        $_.Options -match 'Constant' -or
        $_.Options -match 'ReadOnly'
    } |
    Format-List -Property Name, Value, Options

Creating variables

Create a new variable

This command creates the services variable and stores the results of a Get-Service command in it. Because the current location is in the Variable: drive, the value of the -Path parameter is a dot (.), which represents the current location.

The parentheses around the Get-Service command ensure that the command is executed before the variable is created. Without the parentheses, the value of the new variable is a "Get-Service" string.

New-Item -Path . -Name services -Value (Get-Service)

Create a variable using an absolute path

This command creates a services variable and stores the result of a Get-Service command in it.

New-Item -Path Variable:services -Value Get-Service

To create a variable without a value, omit the assignment operator.

Changing variables

Rename a variable

This command uses the Rename-Item cmdlet to change the name of the a variable to processes.

Rename-Item -Path Variable:a -NewName processes

Change the value of a variable

This command uses the Set-Item cmdlet to change the value of the ErrorActionPreference variable to "Stop".

Set-Item -Path Variable:ErrorActionPreference -Value Stop

Copy a variable

This command uses the Copy-Item cmdlet to copy the processes variable to old_processes. This creates a new variable named old_processes that has the same value as the processes variable.

Copy-Item -Path Variable:processes -Destination Variable:old_processes

Delete a variable

This command deletes the serv variable from the current session. You can use this command in any PowerShell drive.

Remove-Variable -Path Variable:serv

Delete variables using the -Force parameter

This command deletes all variables from the current session except for the variables whose Options property has a value of Constant. Without the -Force parameter, the command does not delete variables whose Options property has a value of ReadOnly.

Remove-Item Variable:* -Force

Setting the value of a variable to null

This command uses the Clear-Item cmdlet to change the value of the processes variable to NULL.

Clear-Item -Path Variable:processes

Using the pipeline

Provider cmdlets accept pipeline input. You can use the pipeline to simplify task by sending provider data from one cmdlet to another provider cmdlet. To read more about how to use the pipeline with provider cmdlets, see the cmdlet references provided throughout this article.

Getting help

Beginning in Windows PowerShell 3.0, you can get customized help topics for provider cmdlets that explain how those cmdlets behave in a file system drive.

To get the help topics that are customized for the file system drive, run a Get-Help command in a file system drive or use the -Path parameter of Get-Help to specify a file system drive.

Get-Help Get-ChildItem

Get-Help Get-ChildItem -Path Variable:

See also