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about_Functions_Advanced

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Short description

Introduces advanced functions that are a way to create cmdlets using scripts.

Long description

A cmdlet is a single command that participates in the pipeline semantics of PowerShell. This includes binary cmdlets, advanced script functions, CDXML, and Workflows.

Advanced functions allow you create cmdlets that are written as a PowerShell function. Advanced functions make it easier to create cmdlets without having to write and compile a binary cmdlet. Binary cmdlets are .NET classes that are written in a .NET language such as C#.

Advanced functions use the CmdletBinding attribute to identify them as functions that act like cmdlets. The CmdletBinding attribute is similar to the Cmdlet attribute that's used in compiled cmdlet classes to identify the class as a cmdlet. For more information about this attribute, see about_Functions_CmdletBindingAttribute.

The following example shows a function that accepts a name and then prints a greeting using the supplied name. Also notice that this function defines a name that includes a verb (Send) and noun (Greeting) pair like the verb-noun pair of a compiled cmdlet. However, functions aren't required to have a verb-noun name.

function Send-Greeting
{
    [CmdletBinding()]
    Param(
        [Parameter(Mandatory=$true)]
        [string] $Name
    )

    Process
    {
        Write-Host ("Hello " + $Name + "!")
    }
}

The parameters of the function are declared using the Parameter attribute. This attribute can be used alone, or it can be combined with the Alias attribute or with several other parameter validation attributes. For more information about how to declare parameters (including dynamic parameters that are added at runtime), see about_Functions_Advanced_Parameters.

The actual work of the previous function is performed in the process block, which is equivalent to the ProcessingRecord method that's used by compiled cmdlets to process the data that's passed to the cmdlet. This block, along with the begin and end blocks, is described in the about_Functions_Advanced_Methods topic.

Advanced functions differ from compiled cmdlets in the following ways:

  • Advanced function parameter binding doesn't throw an exception when an array of strings is bound to a Boolean parameter.
  • The ValidateSet attribute and the ValidatePattern attribute can't pass named parameters.
  • Advanced functions can't be used in transactions.

See also