$re = '/.*thank(\-|\_|)you.*/';
$str = '/thank-you/
/free-estimate/?thank_you=true
/estimate-request/?thank_you=true
/free-estimate/offer1/thank-you.html
/free-estimate/offer2/thank-you.html';
preg_match_all($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