$re = '/^(\w{3}\s{1}\w{3}\s{1}\d{2}\s{1}\d{2}\:\d{2}\:\d{2}\s{1}\d{4})?((\r||.|\n)*)(?=(\w{3}\s{1}\w{3}\s{1}\d{2}\s{1}\d{2}\:\d{2}\:\d{2}\s{1}\d{4}))/m';
$str = 'Tue Sep 14 08:57:47 2021
Thread 1 advanced to log sequence 186 (LGWR switch)
Current log# 2 seq# 186 mem# 0: D:\\ORADB\\DV1\\REDO02A.LOG
Current log# 2 seq# 186 mem# 1: H:\\ORADB\\DV1\\REDO02B.LOG
Tue Sep 14 09:07:40 2021
Thread 1 advanced to log sequence 187 (LGWR switch)
Current log# 3 seq# 187 mem# 0: D:\\ORADB\\DV1\\REDO03A.LOG
Current log# 3 seq# 187 mem# 1: H:\\ORADB\\DV1\\REDO03B.LOG
Tue Sep 14 09:22:09 2021
Thread 1 advanced to log sequence 188 (LGWR switch)
Current log# 4 seq# 188 mem# 0: D:\\ORADB\\DV1\\REDO04A.LOG
Current log# 4 seq# 188 mem# 1: H:\\ORADB\\DV1\\REDO04B.LOG
Tue Sep 14 09:38:03 2021
Thread 1 advanced to log sequence 189 (LGWR switch)
Current log# 1 seq# 189 mem# 0: D:\\ORADB\\DV1\\REDO01A.LOG
Current log# 1 seq# 189 mem# 1: H:\\ORADB\\DV1\\REDO01B.LOG';
preg_match_all($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