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about_Functions_Advanced_Methods

Updated: August 9, 2012

Applies To: Windows PowerShell 2.0, Windows PowerShell 3.0

TOPIC
    about_Functions_Advanced_Methods

SHORT DESCRIPTION
    Describes how functions that specify the CmdletBinding attribute can use
    the methods and properties that are available to compiled cmdlets.

LONG DESCRIPTION
    Functions that specify the CmdletBinding attribute can access a number of 
    methods and properties through the $pscmdlet variable. These methods 
    include the following methods:


        - Input-processing methods that compiled cmdlets use to do their work.

        - The ShouldProcess and ShouldContinue methods that are used to get 
          user feedback before an action is performed.

        - The ThrowTerminatingError method for generating error records.

        - Several Write methods that return different types of output.


    All the methods and properties of the PSCmdlet class are available to 
    advanced functions. For more information about these methods and 
    properties, see System.Management.Automation.PSCmdlet in the MSDN 
    (Microsoft Developer Network) library at 
    http://go.microsoft.com/fwlink/?LinkId=142139.


  Input Processing Methods

      The methods described in this section are referred to as the input 
      processing methods. For functions, these three methods are represented
      by the Begin, Process, and End blocks of the function. Each function 
      must include one or more of these blocks. The Windows PowerShell runtime
      uses the code within these blocks when it is running a function. (These
      blocks are also available to functions that do not use the CmdletBinding
      attribute.)

      
    Begin
      This block is used to provide optional one-time preprocessing for the 
      function. The Windows PowerShell runtime uses the code in this block one
      time for each instance of the function in the pipeline.


    Process
      This block is used to provide record-by-record processing for the 
      function. This block might be used any number of times, or not at all,
      depending on the input to the function. For example, if the function is
      the first command in the pipeline, the Process block will be used one 
      time. If the function is not the first command in the pipeline, the 
      Process block is used one time for every input that the function 
      receives from the pipeline. If there is no pipeline input, the Process 
      block is not used.

      This block must be defined if a function parameter is set to accept 
      pipeline input. If this block is not defined and the parameter accepts
      input from the pipeline, the function will miss the values that are 
      passed to the function through the pipeline. 

      Also, when the function supports confirmation requests (when the 
      SupportsShouldProcess parameter of the Parameter attribute is set to 
      $True), the call to the ShouldProcess method must be made from within
      the Process block.

    End
      This block is used to provide optional one-time post-processing for 
      the function.

      The following example shows the outline of a function that contains a
      Begin block for one-time preprocessing, a Process block for multiple 
      record processing, and an End block for one-time post-processing.

          Function Test-ScriptCmdlet
          {
            [CmdletBinding(SupportsShouldProcess=$True)] 
            Param ($Parameter1)
            Begin{}
            Process{}
            End{}
          }


  Confirmation Methods

    ShouldProcess
      This method is called to request confirmation from the user before the 
      function performs an action that would change the system. The function 
      can continue based on the Boolean value returned by the method. This 
      method can be called only from within the Process{} block of the 
      function. And, the CmdletBinding attribute must declare that the 
      function supports ShouldProcess (as shown in the previous example).

      For more information about this method, see 
      System.Management.Automation.Cmdlet.ShouldProcess in the MSDN library at 
      http://go.microsoft.com/fwlink/?LinkId=142142.

      For more information about how to request confirmation, see 
      "Requesting Confirmation" in the MSDN library at 
      http://go.microsoft.com/fwlink/?LinkID=136658.


    ShouldContinue
      This method is called to request a second confirmation message. It 
      should be called when the ShouldProcess method returns $true. For more
      information about this method, see 
      System.Management.Automation.Cmdlet.ShouldContinue in the MSDN library
      at http://go.microsoft.com/fwlink/?LinkId=142143.


  Error Methods

    Functions can call two different methods when errors occur. When a 
    nonterminating error occurs, the function should call the WriteError 
    method, which is described in the "Write Methods" section. When a 
    terminating error occurs and the function cannot continue, it should call
    the ThrowTerminatingError method. You can also use the Throw statement for
    terminating errors and the Write-Error cmdlet for nonterminating errors.

    For more information, see System.Management.Automation.Cmdlet.
    ThrowTerminatingError in the MSDN libray at 
    http://go.microsoft.com/fwlink/?LinkId=142144.


  Write Methods

      A function can call the following methods to return different types of 
      output. Notice that not all the output goes to the next command in the 
      pipeline. You can also use the various Write cmdlets, such as 
      Write-Error.


    WriteCommandDetail
      For information about the WriteCommandDetails method, see 
      System.Management.Automation.Cmdlet.WriteCommandDetail in the MSDN 
      library at http://go.microsoft.com/fwlink/?LinkId=142155.


    WriteDebug
      To provide information that can be used to troubleshoot a function, 
      make the function call the WriteDebug method. This displays debug 
      messages to the user. For more information, see 
      System.Management.Automation.Cmdlet.WriteDebug in the MSDN library
      at http://go.microsoft.com/fwlink/?LinkId=142156.


    WriteError
      Functions should call this method when nonterminating errors occur and
      the function is designed to continue processing records. For more 
      information, see System.Management.Automation.Cmdlet.WriteError in the 
      MSDN library at http://go.microsoft.com/fwlink/?LinkId=142157.

      Note: If a terminating error occurs, the function should call the 
            ThrowTerminatingError method. 


    WriteObject
      This method allows the function to send an object to the next command in 
      the pipeline. In most cases, this is the method to use when the function
      returns data. For more information, see 
      System.Management.Automation.PSCmdlet.WriteObject in the MSDN library at
      http://go.microsoft.com/fwlink/?LinkId=142158.


    WriteProgress
      For functions whose actions take a long time to complete, this method 
      allows the function to call the WriteProgress method so that progress
      information is displayed. For example, you can display the percent 
      completed. For more information, see 
      System.Management.Automation.PSCmdlet.WriteProgress in the MSDN library
      at http://go.microsoft.com/fwlink/?LinkId=142160.


    WriteVerbose
      To provide detailed information about what the function is doing, make 
      the function call the WriteVerbose method to display verbose messages to
      the user. By default, verbose messages are not displayed. For more 
      information, see System.Management.Automation.PSCmdlet.WriteVerbose
      in the MSDN library at http://go.microsoft.com/fwlink/?LinkId=142162.

    WriteWarning
      To provide information about conditions that may cause unexpected 
      results, make the function call the WriteWarning method to display 
      warning messages to the user. By default, warning messages are displayed.
      For more information, see 
      System.Management.Automation.PSCmdlet.WriteWarning in the MSDN library 
      at http://go.microsoft.com/fwlink/?LinkId=142164.

      Note: You can also display warning messages by configuring the 
            WarningPreference variable or by using the Verbose and Debug 
            command-line options.


  Other Methods and Properties

      For information about the other methods and properties that can be 
      accessed through the $PSCmdlet variable, see 
      System.Management.Automation.PSCmdlet in the MSDN library at
      http://go.microsoft.com/fwlink/?LinkId=142139. 

      For example, the ParameterSetName property allows you to see the parameter 
      set that is being used. Parameter sets allow you to create a function that 
      performs different tasks based on the parameters that are specified when 
      the function is run.


SEE ALSO
    about_Functions
    about_Functions_Advanced
    about_Functions_Advanced_Parameters
    about_Functions_CmdletBindingAttribute
    about_Functions_OutputTypeAttribute



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