about_Throw

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