$re = '/\d{2}\/[a-zA-Z]{3}\/\d{4}|\d{2}\/\d{2}\/\d{4}/';
$str = '20/dec/2018
30/mar/2017
30/03/2017
29/feb/2000';
preg_match_all($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