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ABOUT SCRIPT BLOCKS
Short description
Defines what a script block is and explains how to use script blocks in the
PowerShell programming language.
Long description
In the PowerShell programming language, a script block is a collection of
statements or expressions that can be used as a single unit. A script block
can accept arguments and return values.
Syntactically, a script block is a statement list in braces, as shown in
the following syntax:
{<statement list>}
A script block returns the output of all the commands in the script block,
either as a single object or as an array.
You can also specify a return value using the return keyword. The return
keyword does not affect or suppress other output returned from your script
block. However, the return keyword exits the script block at that line. For
more information, see about_Return.
Like functions, a script block can include parameters. Use the Param
keyword to assign named parameters, as shown in the following syntax:
{
Param([type]$Parameter1 [,[type]$Parameter2])
<statement list>
}
[!NOTE] In a script block, unlike a function, you cannot specify
parameters outside the braces.
Like functions, script blocks can include the DynamicParam, Begin, Process,
and End keywords. For more information, see about_Functions and
about_Functions_Advanced.
Using Script Blocks
A script block is an instance of a Microsoft .NET Framework type
System.Management.Automation.ScriptBlock. Commands can have script block
parameter values. For example, the Invoke-Command cmdlet has a ScriptBlock
parameter that takes a script block value, as shown in this example:
Invoke-Command -ScriptBlock { Get-Process }
Handles NPM(K) PM(K) WS(K) VM(M) CPU(s) Id ProcessName
------- ------ ----- ----- ----- ------ -- -----------
999 28 39100 45020 262 15.88 1844 communicator
721 28 32696 36536 222 20.84 4028 explorer
...
Invoke-Command can also execute script blocks that have parameter blocks.
Parameters are assigned by position using the ARGUMENTLIST parameter.
Invoke-Command -ScriptBlock { param($p1, $p2)
"p1: $p1"
"p2: $p2"
} -ArgumentList "First", "Second"
p1: First
p2: Second
The script block in the preceding example uses the param keyword to create
a parameters $p1 and $p2. The string "First" is bound to the first
parameter ($p1) and "Second" is bound to ($p2).
For more information about the behavior of ARGUMENTLIST, see
about_Splatting.
You can use variables to store and execute script blocks. The example below
stores a script block in a variable and passes it to Invoke-Command.
$a = { Get-Service BITS }
Invoke-Command -ScriptBlock $a
Status Name DisplayName
------ ---- -----------
Running BITS Background Intelligent Transfer Ser...
The call operator is another way to execute script blocks stored in a
variable. Like Invoke-Command, the call operator executes the script block
in a child scope. The call operator can make it easier for you to use
parameters with your script blocks.
$a ={ param($p1, $p2)
"p1: $p1"
"p2: $p2"
}
&$a -p2 "First" -p1 "Second"
p1: Second
p2: First
You can store the output from your script blocks in a variable using
assignment.
PS> $a = { 1 + 1}
PS> $b = &$a
PS> $b
2
PS> $a = { 1 + 1}
PS> $b = Invoke-Command $a
PS> $b
2
For more information about the call operator, see about_Operators.
Using delay-bind script blocks with parameters
A typed parameter that accepts pipeline input (by Value) or
(by PropertyName) enables use of DELAY-BIND script blocks on the parameter.
Within the DELAY-BIND script block, you can reference the piped in object
using the pipeline variable $_.
# Renames config.log to old_config.log
dir config.log | Rename-Item -NewName {"old_" + $_.Name}
In more complex cmdlets, delay-bind script blocks allow the reuse of one
piped in object to populate other parameters.
Notes on DELAY-BIND script blocks as parameters:
- You must explicitly specify any parameter names you use with DELAY-BIND
script blocks.
- The parameter must not be untyped, and the parameter's type cannot be
[scriptblock] or [object].
- You receive an error if you use a DELAY-BIND script block without
providing pipeline input.
Rename-Item -NewName {$_.Name + ".old"}
Rename-Item : Cannot evaluate parameter 'NewName' because its argument is
specified as a script block and there is no input. A script block cannot
be evaluated without input.
At line:1 char:23
+ Rename-Item -NewName {$_.Name + ".old"}
+ ~~~~~~~~~~~~~~~~~~
+ CategoryInfo : MetadataError: (:) [Rename-Item],
ParameterBindingException
+ FullyQualifiedErrorId : ScriptBlockArgumentNoInput,
Microsoft.PowerShell.Commands.RenameItemCommand
See Also
about_Functions
about_Functions_Advanced
about_Operators