$re = '/(?:\d{4}-\d{2}-\d{2})(.*)/m';
$str = '2020-04-14 17:00:00
2012-01-01T17:52:27.8116975-12:00
2012-02-01T18:21:06
2012-03-01T00:00:00Z';
preg_match_all($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