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).
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