$re = '/^\w+([-+.\']\w+)*@\w+([-.]\w+)*\.[A-Z0-9]{2,6}([-.][A-Z0-9]{2,6})*$/i';
$str = 'thomas-o\'leary@upenn.com';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($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