$re = '/_2020\d{4}_|\./m';
$str = '_20201007144100_20200416_reg.zip
_20201007103200_20201007.zip
_20201007095000_20201007.zip
_20201007092933_20201007.zip
_20201007061717_20201007_txn.zip
_20201007041719_20201007.zip';
preg_match_all($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