$re = '/(?<MM>[01]?[0-9])\/(?<DD>[0-3]?[0-9])\/(?<YYYY>[0-2][0-9][0-9][0-9])/m';
$str = 'mm/dd/yyyy Examples
01/01/2020 #1st Jan
07/03/2020 #3 July
12/2/2020 #2 December
4/23/2020 #23 April
19/39/2020
';
preg_match_all($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