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Extending Output Objects

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You can extend the .NET Framework objects that are returned by cmdlets, functions, and scripts by using types files (.ps1xml). Types files are XML-based files that let you add properties and methods to existing objects. For example, Windows PowerShell provides the Types.ps1xml file, which adds elements to several existing .NET Framework objects. The Types.ps1xml file is located in the Windows PowerShell installation directory ($pshome). You can create your own types file to further extend those objects or to extend other objects. When you extend an object by using a types file, any instance of the object is extended with the new elements.

Extending the System.Array Object

The following example shows how Windows PowerShell extends the System.Array object in the Types.ps1xml file. By default, System.Array objects have a Length property that lists the number of objects in the array. However, because the name "length" does not clearly describe the property, Windows PowerShell adds the Count alias property, which displays the same value as the Length property. The following XML adds the Count property to the System.Array type.

<Type>
  <Name>System.Array</Name>
  <Members>
    <AliasProperty>
      <Name>Count</Name>
      <ReferencedMemberName>Length</ReferencedMemberName>
    </AliasProperty>
  </Members>
</Type>

To see this new alias property, use a Get-Member command on any array, as shown in the following example.

Get-Member -InputObject (1,2,3,4)

The command returns the following results.

Name           MemberType    Definition
----           ----------    ----------
Count          AliasProperty Count = Length
Address        Method        System.Object& Address(Int32 )
Clone          Method        System.Object Clone()
CopyTo         Method        System.Void CopyTo(Array array, Int32 index):
Equals         Method        System.Boolean Equals(Object obj)
Get            Method        System.Object Get(Int32 )
...
Length         Property      System.Int32 Length {get;}

You can use either the Count property or the Length property to determine how many objects are in an array. For example:

PS> (1, 2, 3, 4).Count

4

PS> (1, 2, 3, 4).Length

4

Custom Types Files

To create a custom types file, start by copying an existing types file. The new file can have any name, but it must have a .ps1xml file name extension. When you copy the file, you can place the new file in any directory that is accessible to Windows PowerShell, but it is useful to place the files in the Windows PowerShell installation directory ($pshome) or in a subdirectory of the installation directory.

To add your own extended types to the file, add a types element for each object that you want to extend. The following topics provide examples.

After you define your own extended types, use one of the following methods to make your extended objects available:

  • To make your extended types file available to the current session, use the Update-TypeData cmdlet to add the new file. If you want your types to take precedence over the types that are defined in other types files (including the Types.ps1xml file), use the PrependData parameter of the Update-TypeData cmdlet.
  • To make your extended types file available to all future sessions, add the types file to a module, export the current session, or add the Update-TypeData command to your Windows PowerShell profile.

Signing Types Files

Types files should be digitally signed to prevent tampering because the XML can include script blocks. For more information about adding digital signatures, see about_Signing

See Also

Defining Default Properties for Objects

Defining Default Methods for Objects

Defining Default Member Sets for Objects

Writing a Windows PowerShell Cmdlet