Windows PowerShell introduced parameter validation which drastically reduces lines of validation code – and replaces it with a couple of markup tags:
ValidateCount (int minLength, int maxlength)
How many arguments are allowed for a parameter.
[ValidateCount(1,3)]
[String[]]
$Collection
ValidateLength (int minLength, int maxlength)
Length (in characters) of a parameter argument.
[ValidateLength(1,8)]
[String[]]
$Phone
ValidatePattern (string regexString, Named Parameters)
Valid patterns for a parameter argument.
[ValidatePattern("[0-9][0-9][0-9][0-9]")]
[String[]]
$Pin
ValidateRange (object minRange, object maxRange)
Valid range for a parameter argument.
[ValidateRange(18,120)]
[Int]
$Number
ValidateSet (string[] validValues, Named Parameters)
Possible values for a parameter argument.
[ValidateSet("One","Two","Three","Four")]
[String]
$TextString
ValidateScript (scriptblock validValues)
Custom script for validation
[ValidateScript({Test-Path $_ -PathType 'Container'})]
[String]
$Path
ValidateNotNull ()
Input is not null
[ValidateNotNull()]
[String]
$Id
ValidateNotNullOrEmpty ()
Input is neither null or empty
[ValidateNotNullOrEmpty()]
[String[]]
$UserName
Read more about validating parameters on MSDN:
Or use PowerShell built-in help: