My Book some text Another Book EOF; echo preg_replace_callback('/(href=")book-online(\?cid=)([^"]+)"/i', function($m) { static $idmap = array("123" => "321", "645" => "546"); return $m[1] . 'Book-online.htm' . $m[2] . $idmap[$m[3]]; }, $content) . "\n"; ?>