How to preg_match a variable which can be NULL in PHP?

Question

I got a problem with the PHP function preg_match today.

I want to match exact 12 characters in a string ($test='123456789012') OR $test = NULL

My problem is the OR NULL call how is the RegEx for this NULL variable.

Tried: preg_match("/^([\w.-]{12})|(NULL)$/",$test);

Answer 1

A NULL value is not a string literal with the letters NULL, so if you're searching for NULL when something is NULL they will never match.

You can do

if($test)
    preg_match("/^([\w.-]{12})$/",$test);
else
    //whatever works