$re = '/.*?((?=Part1)|(?=Part2))|(?=Part3)|(?=Part4)/';
$str = 'MatchOnlyMe! Part1 Part2 Part3 Part4
MatchOnlyMe! Part2 Part3 Part4
MatchOnlyMe! Part2 Part3
MatchOnlyMe! Part1 Part3 Part4
MatchOnlyMe! Part3 Part4
MatchOnlyMe! Part4
MatchOnlyMe! Part2
MatchOnlyMe! Part2 Part4
MatchOnlyMe! Part1 Part4
MatchOnlyMe! Part1 Part2 Part4';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php