<?php
function siteURL()
{
return "http://www.luntech.com?dev=desktop&name=value";
}
define('SITE_URL', siteURL()); //returns http://example.com/dir/
define('CKEDITOR', 'http://m.luntech.com/default.asp?dev=mobile&name=value');
// ignore the previous code is just to emulate your constants and functions
// the answer is the following line:
echo str_replace(SITE_URL,'',CKEDITOR);
?>