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about_Simplified_Syntax

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Short description

Describes easier, more natural-language ways of scripting filters for collections of objects.

Long description

Simplified syntax, introduced in Windows PowerShell 3.0, lets you build some filter commands without using script blocks. The simplified syntax more closely resembles natural language, and is primarily useful with collections of objects that get piped into commands Where-Object and ForEach-Object or their corresponding aliases where and foreach.

You can use a method on the members of a collection (most commonly, an array) without referring to the automatic variable $_ inside a script block.

Consider the following two invocations:

Standard Syntax

Get-ChildItem Cert:\LocalMachine\Root |
    Where-Object -FilterScript { $_.FriendlyName -eq 'Verisign' }
Get-ChildItem Cert:\ -Recurse |
    ForEach-Object -FilterScript { $_.GetKeyAlgorithm() }

Note

In the second command, the GetKeyAlgorithm method is called on each object in the collection. If the object received from the pipeline doesn't have a GetKeyAlgorithm method, the command produces an error.

Simplified syntax

Under the simplified syntax, comparison operators that work on members of objects in a collection are implemented as parameters. Also, you can invoke a method on objects in a collection without referring to the automatic variable $_ inside a script block. Compare the following two invocations to the standard syntax examples:

Get-ChildItem Cert:\LocalMachine\Root |
    Where-Object -Property FriendlyName -EQ 'Verisign'
Get-ChildItem Cert:\ -Recurse |
    ForEach-Object -MemberName GetKeyAlgorithm

Since the Property and MemberName parameters are positional, you can omit them from the command. Using aliases, you can further simplify the commands:

dir Cert:\LocalMachine\Root | Where FriendlyName -EQ 'Verisign'
dir Cert:\ -Recurse | ForEach GetKeyAlgorithm

While both syntaxes work, the simplified syntax returns results without referring to the automatic variable $_ inside a script block. The simplified syntax reads more like a natural language statement and can be easier to understand.

The method name GetKeyAlgorithm is passed as an argument for the MemberName parameter of ForEach-Object. When you invoke the method using the simplified syntax, the method is called for each object in pipeline only if that object has that method. Therefore, you get the same results, but without errors.

In the next example, Description is passed to the MemberName parameter of ForEach-Object. The command displays the description of each System.Diagnostics.Process object returned by Get-Process.

Get-Process | foreach Description

In this example, the method name GetFiles is passed to the MemberName parameter of the ForEach-Object command. The .* value is passed to the ArgumentList parameter. The GetFiles() method is called with the search pattern parameter .* for each System.IO.DirectoryInfo object returned by Get-ChildItem.

Get-ChildItem /home -Directory | foreach GetFiles .*

See also