<?php

$myStr = "some words that are cool";
$myWords = array('words', 'cool');
$myWordString = join('|', $myWords);

$myRegex = "/(^|[\s.,])(" . $myWordString . ")([\s.,]|$)/iu";

print("Regexp is: " . $myRegex . "\n");
preg_match_all($myRegex, $myStr, $myRes);
var_dump($myRes[2]);

?>