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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.
- Get-Location
- Set-Location
- Get-Item
- New-Item
- Remove-Item
- Clear-Item
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.
- Get-Variable
- New-Variable
- Set-Variable
- Remove-Variable
- Clear-Variable
[!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, $p = Get-Process creates the p variable and
stores the results of a Get-Process command in it.
Types exposed by this provider
Variables can be one of several different types. Most variables will be
instances of the PSVariable class. Other variables and their types are
listed below.
- The ? variable is an instance of the QuestionMarkVariable class.
- The null variable is an instance of the NullVariable class.
- The maximum count variables are instances of the
SessionStateCapacityVariable class.
- LocalVariable instances contain information about current execution,
such as:
- MyInvocation
- PSCommandPath
- PSScriptRoot
- PSBoundParameters
- args
- input
Navigating the Variable drives
The VARIABLE provider exposes its data store in the Variable: drive. To
work with variables, you can change your location to the Variable: drive
(Set-Location Variable:), or you can work from any other PowerShell drive.
To reference a variable from another location, use the drive name
(Variable:) in the path.
Set-Location Variable:
To return to a file system drive, type the drive name. For example, type:
Set-Location C:
You can also work with the VARIABLE provider from any other PowerShell
drive. To reference an variable from another location, use the drive name
Variable: in the path.
[!NOTE] PowerShell uses aliases to allow you a familiar way to work with
provider paths. Commands such as dir and ls are now aliases for
Get-ChildItem, cd is an alias for Set-Location. and pwd is an alias for
Get-Location.
Displaying the value of variables
Get all variables in the current session
This command gets the list of all the variables and their values in the
current session. You can use this command from any PowerShell drive.
Get-ChildItem -Path Variable:
Get a variable using its provider path
This command retrieves a variables value using its provider path prefixed
by the dollar sign ($). 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
about_Variables
about_Automatic_Variables
about_Providers