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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) [], R
untimeException
+ 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 (Pow
erShell):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\*.xml -recurse |
sort lastwritetime |
ft lastwritetime, attributes, name -auto
}
SEE ALSO
about_Break
about_Continue
about_Scopes
about_Trap
about_Try_Catch_Finally