$re = '/([0-9]{4})\.([0-9]{2})\.([0-9]{2})/';
$str = '2017.10.02
2015.08.09
2017-05-02
20190908
log-2017.10.02
notification-2015.08.09-name';
preg_match_all($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