about_Throw

Applies To: Windows PowerShell 2.0

TOPIC
    about_Throw

SHORT DESCRIPTION
    Describes the Throw keyword, which generates a terminating error.

LONG DESCRIPTION
    The Throw keyword causes a terminating error. You can use the Throw keyword
    to stop the processing of a command, function, or script. 

    For example, you can use the Throw keyword in the script block of an If
    statement to respond to a condition or in the Catch block of a
    Try-Catch-Finally statement. You can also use the Throw keyword in a
    parameter declaration to make a function parameter mandatory. 

    The Throw keyword can throw any object, such as a user message string or
    the object that caused the error. 


  SYNTAX

    The syntax of the Throw keyword is as follows:

        throw [<expression>]


    The expression in the Throw syntax is optional. When the Throw statement
    does not appear in a Catch block, and it does not include an expression, 
    it generates a ScriptHalted error.

        C:\PS> throw

        ScriptHalted
        At line:1 char:6
        + throw <<<<
            + CategoryInfo          : OperationStopped: (:) [], RuntimeException
            + FullyQualifiedErrorId : ScriptHalted


    If the Throw keyword is used in a Catch block without an expression, it
    throws the current RuntimeException again. For more information, see
    about_Try_Catch_Finally.


  THROWING A STRING

    The optional expression in a Throw statement can be a string, as shown in
    the following example: 

        C:\PS> throw "This is an error."

        This is an error.
        At line:1 char:6
        + throw <<<<  "This is an error."
            + CategoryInfo          : OperationStopped: (This is an error.:String) [], RuntimeException
            + FullyQualifiedErrorId : This is an error.


  THROWING OTHER OBJECTS

    The expression can also be an object that throws the object that represents
    the PowerShell process, as shown in the following example:

        C:\PS> throw (get-process powershell)

        System.Diagnostics.Process (powershell)
        At line:1 char:6
        + throw <<<<  (get-process powershell)
            + CategoryInfo          : OperationStopped: (System.Diagnostics.Process (powershell):Process) [], 
                        RuntimeException
            + FullyQualifiedErrorId : System.Diagnostics.Process (powershell)

    You can use the TargetObject property of  the ErrorRecord object in the 
    $error automatic variable to examine the error.


        C:\PS> $error[0].targetobject

        Handles  NPM(K)    PM(K)      WS(K) VM(M)   CPU(s)     Id ProcessName                                                            
        -------  ------    -----      ----- -----   ------     -- -----------                                                            
            319      26    61016      70864   568     3.28   5548 powershell           


    You can also throw an ErrorRecord object or a Microsoft .NET Framework 
    exception. The following example uses the Throw keyword to throw a
    System.FormatException object.

        C:\PS> $formatError = new-object system.formatexception

        C:\PS> throw $formatError

        One of the identified items was in an invalid format.
        At line:1 char:6
        + throw <<<<  $formatError
            + CategoryInfo          : OperationStopped: (:) [], FormatException
            + FullyQualifiedErrorId : One of the identified items was in an invalid format.


  RESULTING ERROR

    The Throw keyword can generate an ErrorRecord object. The Exception 
    property of the ErrorRecord object contains a RuntimeException object.
    The remainder of the ErrorRecord object and the RuntimeException object
    vary with the object that the Throw keyword throws.

    The RunTimeException object is wrapped in an ErrorRecord object, and the
    ErrorRecord object is automatically saved in the $Error automatic variable.


  USING THROW TO CREATE A MANDATORY PARAMETER

    You can use the Throw keyword to make a function parameter mandatory. 

    This is an alternative to using the Mandatory parameter of the Parameter
    keyword. When you use the Mandatory parameter, the system prompts the user
    for the required parameter value. When you use the Throw keyword, the
    command stops and displays the error record.

    For example, the Throw keyword in the parameter subexpression makes the
    Path parameter a required parameter in the function. 

    In this case, the Throw keyword throws a message string, but it is the
    presence of the Throw keyword that generates the terminating error if
    the Path parameter is not specified. The expression that follows Throw
    is optional.

        function Get-XMLFiles
        {
            param ($path = $(throw "The Path parameter is required."))
            dir -path $path\* -include *.xml -recurse | sort lastwritetime | ft lastwritetime, attributes, name  -auto
        }


SEE ALSO
    about_Break
    about_Continue
    about_Scope
    about_Trap
    about_Try_Catch_Finally