Mastering Windows PowerShell Scripting - Third Edition

The ValidateSet attribute

ValidateSet tests whether the specified argument, or each of an array of arguments, exists in a set of possible values:

function Test-ValidateSet {    [CmdletBinding()]    param (        [ValidateSet('One', 'Two', 'Three')]        [String]$Value    )}

The set of values must be hardcoded in the attribute, it cannot be derived from a variable or another command. By default, the set is not case-sensitive. If it is desirable, the set can be made case-sensitive by using the IgnoreCase named parameter:

function Test-ValidateSet {    [CmdletBInding()]    param (        [ValidateSet('One', 'Two', 'Three', IgnoreCase = $false)]        [String]$Value    )}

Like ValidatePattern and ValidateSet, ValidateSet gains an optional ErrorMessage parameter in PowerShell Core.