TOPIC
about_Variables
SHORT DESCRIPTION
Describes how variables store values that can be used in Windows
PowerShell.
LONG DESCRIPTION
You can store all types of values in Windows PowerShell variables.
They are typically used to store the results of commands and to
store elements that are used in commands and expressions, such as
names, paths, settings, and values.
A variable is a unit of memory in which values are stored. In Windows
PowerShell, variables are represented by text strings that begin
with a dollar sign ($), such as $a, $process, or $my_var.
Variable names are not case-sensitive. Variable names can include
spaces and special characters, but these are difficult to use and
should be avoided.
There are several different types of variables in Windows PowerShell.
-- User-created variables: User-created variables are created and
maintained by the user. By default, the variables that you create at
the Windows PowerShell command line exist only while the Windows
PowerShell window is open, and they are lost when you close the window.
To save a variable, add it to your Windows PowerShell profile. You can
also create variables in scripts with global, script, or local scope.
-- Automatic variables: Automatic variables store the state of
Windows PowerShell. These variables are created by Windows PowerShell,
and Windows PowerShell changes their values as required to maintain
their accuracy. Users cannot change the value of these variables.
For example, the $PSHome variable stores the path to the Windows
PowerShell installation directory.
For more information, a list, and a description of the automatic
variables, see about_Automatic_Variables.
-- Preference variables: Preference variables store user preferences for
Windows PowerShell. These variables are created by Windows PowerShell
and are populated with default values. Users can change the values of
these variables. For example, the $MaximumHistoryCount variable
determines the maximum number of entries in the session history.
For more information, a list, and a description of the preference
variables, see about_Preference_Variables.
WORKING WITH VARIABLES
To create a new variable, use an assignment statement to assign
a value to the variable. You do not have to declare the variable
before using it. The default value of all variables is $null.
For example:
PS> $MyVariable = 1, 2, 3
PS> $path = "C:\Windows\System32"
Variables are very useful for storing the results of commands.
For example:
PS> $processes = Get-Process
PS> $Today = (Get-Date).date
To display the value of a variable, type the variable name, preceded
by a dollar sign ($).
For example:
PS> $MyVariable
1
2
3
PS> $Today
Thursday, September 03, 2009 12:00:00 AM
To change the value of a variable, assign a new value to the variable.
The following examples displays the value of the $MyVariable variable,
changes the value of the variable, and then displays the new value.
PS> $MyVariable
1
2
3
PS> $MyVariable = "The green cat."
PS> $MyVariable
The green cat.
To delete the value of a variable, use the Clear-Variable cmdlet or
change the value to $null.
PS> Clear-Variable -name MyVariable
-or-
PS> $MyVariable = $null
To delete the variable, use the Remove-Variable or Remove-Item
cmdlets. (These cmdlets are discussed later in this topic.)
PS> remove-variable -name MyVariable
PS> remove-item -path variable:\myvariable
To get a list of all of the variables in your Windows PowerShell
session, type:
get-variable
TYPES OF VARIABLES
You can store any type of object in a variable, including integers,
strings, arrays, hash tables, and objects that represent processes,
services, event logs, and computers.
Windows PowerShell variables are "loosely typed," which means that
they are not limited to a particular type of object. A single variable
can even contain a collection (an "array") of different types of objects
at the same time.
The data type of a variable, which is a .NET Framework type, is
determined by the .NET types of the values of the variable.
For example:
PS> $a = 12 (System.Int32)
PS> $a = "Word" (System.String)
PS> $a = 12, "Word" (System.Int32, System.String)
PS> $a = dir C:\Windows\System32 (Files and folders)
You can use a type attribute and cast notation to ensure that a
variable can contain only objects of the specified type or objects
that can be converted to that type. If you try to assign a value
of another type, Windows PowerShell tries to convert the value to
its type. If it cannot, the assignment statement fails.
To use cast notation, enter a type name, enclosed in brackets, before
the variable name (on the left side of the assignment statement).
The following example creates an $number variable that can contain
only integers, a $words variable that can contain only strings, and
a $dates variable that can contain only DateTime objects.
PS> [int]$number = 8
PS> $a = "12345" (The string is converted to an integer.)
PS> $a = "Hello"
Cannot convert value "Hello" to type "System.Int32". Error: "Input string was not in a correct format."
At line:1 char:3
+ $a <<<< = "Hello"
+ CategoryInfo : MetadataError: (:) [], ArgumentTransformationMetadataException
+ FullyQualifiedErrorId : RuntimeException
PS> [string]$words = "Hello"
PS> $words = 2 (The integer is converted to a string.)
PS> $words + 10 (The strings are concatenated.)
210
PS> [datetime] $dates = "09/12/91" (The string is converted to a DateTime object.)
PS> $dates
Thursday, September 12, 1991 12:00:00 AM
PS> $dates = 10 (The integer is converted to a DateTime object.)
PS> $dates
Monday, January 01, 0001 12:00:00 AM
USING VARIABLES IN COMMANDS AND EXPRESSIONS
To use a variable in a command or expression, type the variable name,
preceded by the dollar sign ($).
If the variable name (and dollar sign) are not enclosed in quotation marks,
or if they are enclosed in double quotation marks ("), the value of the
variable is used in the command or expression.
If the variable name (and dollar sign) are enclosed in single quotation
marks, ('), the variable name is used in the expression.
For example, the first command gets the value of the $profile variable,
which is the path to the Windows PowerShell user profile file in the Windows
PowerShell console. The second command opens the file in Notepad, and the
third and fourth commands use the name of the variable in an expression.
PS> $profile
C:\Documents and Settings\User01\My Documents\WindowsPowerShell\Microsoft.PowerShell_profile.ps1
PS> noteapd $profile
- or -
PS> notepad "$profile"
C:\Documents and Settings\User01\My Documents\WindowsPowerShell\Microsoft.PowerShell_profile.ps1
PS> '$profile'
$profile
PS> 'Use the $profile variable.'
Use the $profile variable.
For more information about using quotation marks in Windows PowerShell, see
about_Quoting_Rules.
VARIABLE NAMES THAT INCLUDE SPECIAL CHARACTERS
Variable names begin with a dollar sign. They can include
alphanumeric characters and special characters. The length
of the variable name is limited only by available memory.
Whenever possible, variable names should include only
alphanumeric characters and the underscore character (_).
Variable names that include spaces and other special characters,
are difficult to use and should be avoided.
To create or display a variable name that includes spaces or
special characters, enclose the variable name in braces. This directs
Windows PowerShell to interpret the characters in the variable name
literally.
For example, the following command creates and then displays a variable
named "save-items".
C:\PS> ${save-items} = "a", "b", "c"
C:\PS> ${save-items}
a
b
c
The following command gets the child items in the directory that is
represented by the "ProgramFiles(x86)" environment variable.
C:\PS> Get-childitem ${env:ProgramFiles(x86)}
To refer to a variable name that includes braces, enclose the
variable name in braces, and use the backtick (escape) character
to escape the braces. For example, to create a variable
named "this{value}is" with a value of 1, type:
C:\PS> ${this`{value`}is} = 1
C:\PS> ${this`{value`}is}
1
VARIABLES AND SCOPE
By default, variables are available only in the scope in which
they are created.
For example, a variable that you create in a function is
available only within the function. A variable that you
create in a script is available only within the script (unless
you dot-source the script, which adds it to the current scope).
You can use a scope modifier to change the default scope of the
variable. The following expression creates a variable named
"Computers". The variable has a global scope, even when it is
created in a script or function.
$global:computers = "Server01"
For more information, see about_Scopes.
SAVING VARIABLES
Variables that you create are available only in the session in which
you create them. They are lost when you close your session.
To create the in every Windows PowerShell session that you start,
add the variable to your Windows PowerShell profile.
For example, to change the value of the $VerbosePreference variable in
every Windows PowerShell session, add the following command to your Windows
PowerShell profile.
$VerbosePreference = "Continue"
You can add this command to your profile by opening the profile file in a
text editor, such as Notepad. For more information about Windows PowerShell
profiles, see about_profiles.
THE VARIABLE: DRIVE
Windows PowerShell Variable provider creates a Variable: drive that
looks and acts like a file system drive, but it contains the variables
in your session and their values.
To change to the variable: drive, type:
set-location variable:
(or "cd variable:")
To list the items (variables) in the Variable: drive, use the
Get-Item or Get-ChildItem cmdlets. For example:
get-childitem variable:
(or "dir" or "ls")
To get the value of a particular variable, use file system notation
to specify the name of the drive and the name of the variable. For
example, to get the $PSCulture automatic variable, use the following
command.
get-item variable:\PSCulture
Name Value
---- -----
PSCulture en-US
For more information about the Variable: drive and the Windows
PowerShell Variable provider, type "get-help variable".
THE VARIABLE CMDLETS
Windows PowerShell includes a set of cmdlets that are designed to
manage variables.
Cmdlet Name Description
----------- -----------
Clear-Variable Deletes the value of a variable.
Get-Variable Gets the variables in the current console.
New-Variable Creates a new variable.
Remove-Variable Deletes a variable and its value.
Set-Variable Changes the value of a variable.
To get help for these cmdlets, type: "Get-Help <cmdlet-hame>".
SEE ALSO
about_Automatic_Variables
about_Environment_Variables
about_Preference_Variables
about_Profiles
about_Quoting_Rules
about_Scopes
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