What is regularexpression to allow specific characters in php

Question

i want to allow only characters X,N,-,(Space) to string which user inputs.

Ex : XXXX-NNNNN XXXXXX-NNNN is valid string but Ex XXXx-1NNN XXXX-NNNN is not valid string.

I have found so many regexp for that but didn't find helpful solution

I want this solution in zend form

Answer 1

Try this:

preg_match("/^[XN -]+$/", $string);