ValidateScript Attribute Declaration

The ValidateScript attribute specifies a script that's used to validate a parameter or variable value. PowerShell pipes the value to the script, and generates an error if the script returns $false or if the script throws an exception.

When you use the ValidateScript attribute, the value that's being validated is mapped to the $_ variable. You can use the $_ variable to refer to the value in the script.

Syntax

[ValidateScriptAttribute(ScriptBlock scriptBlock)]
[ValidateScriptAttribute(ScriptBlock scriptBlock, Named Parameters)]

Parameters

• scriptBlock - (System.Management.Automation.ScriptBlock) Required. The script block used to validate the input.
• ErrorMessage - Optional named parameter - The item being validated and the validating scriptblock are passed as the first and second formatting arguments.

Note

The ErrorMessage argument was added in PowerShell 6.

Remarks

• This attribute can be used only once per parameter.
• If this attribute is applied to a collection, each element in the collection must match the pattern.
• The ValidateScript attribute is defined by the System.Management.Automation.ValidateScriptAttribute class.

See Also

System.Management.Automation.ValidateScriptAttribute

Writing a Windows PowerShell Cmdlet