$re = '/^(?:(?=.*[a])(?:(?=.*[b])(?=.*(?:[c]|[d]|[e]))|(?=.*[c])(?=.*(?:[d]|[e])))|(?=.*[d])(?=.*[e])|(?=.*[b])(?:(?=.*[c])(?=.*[d])|(?=.*([c]|[d]))(?=.*[e]))|(?=.*[c])(?=.*[d])(?=.*[e])).*$/m';
$str = 'abcde
edcba
cbdae
bdeac
aaabbb
abc
abd
abe
acd
ace
ade
bcd
bce
bde
cde
';
preg_match_all($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