- var_dump: documentation ( source)
- preg_match: documentation ( source)
<?php
$string = "namespace Concrete\Package\Derp\MenuItems\Derp;";
$regex = "/^namespace\\s+Concrete\\\\Package\\\\[^\\\\]+\\\\(.+?)(?:\\\\.+)?;$/i";
$results = array();
preg_match($regex, $string, $results);
var_dump($results);