$re = '/mon[a-z\.]*\s+|tue[a-z\.]*\s+|wed[a-z\.]*\s+|thu[a-z\.]*\s+|fri[a-z\.]*\s+|sat[a-z\.]*\s+|sun[a-z\.]*\s+/';
$str = '';
preg_match($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