<?php

$string = "orders,items,friends,students OrdeRs or orders OR stuDents or FrIends or students";

preg_match_all('/(orders|items|friends|students)/i', $string, $result, PREG_PATTERN_ORDER);
for ($i = 0; $i < count($result[1]); $i++) {
	echo $result[1][$i]."\n";
}