A couple of different ways exist to transform your scripts into GUI form. If you need to create real GUI tools to interact with the user in PowerShell you're probably going to choose either Windows ...

As Brien demonstrates, string validation is not the only type of input validation that PowerShell can perform.

If your automated script takes action based on a value, it's critical to make sure the value is correct. Good thing PowerShell has ways to validate the values that are passed to a function.