$re = '/^\d{4}\-\d{2}\-\d{2} \d{2}:\d{2}:\d{2}\,\d{3} \w+ [\w\-\.]+ \[(?<myField>[a-zA-Z]+)\]/m';
$str = '2020-04-21 23:59:59,093 INFO xxxx.xxxxx-zz-00000xxx111 [process] start[ppp] time[00] tag[xxx]
2020-04-21 23:59:59,093 INFO xx.xxx-zz-00000x [report] start[ppp] time[00] tag[xxx]';
preg_match_all($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