$re = '/\"(?<Event_Log>[^\"]+)\"/m';
$str = '2021-12-04T01:29:48.015524+00:00 USHCO-EXXON, ipsec-ike-down, 689, "IKE connection with peer 10.218.42.113 (routing-instance EXXON-Control-VR) is up", USPAB
2021-12-04T01:29:15.007722+00:00 USHCO-EXXON, ipsec-tunnel-down, 687, "IPSEC tunnel with peer 10.218.42.111 (routing-instance EXXON-Control-VR) is up", USPAB
2021-12-04T01:29:15.007722+00:00 USHCO-EXXON, ipsec-ike-down, 686, "IKE connection with peer 10.218.42.111 (routing-instance EXXON-Control-VR) is up", USPAB
2021-12-04T01:29:14.807814+00:00 USHCO-EXXON, ipsec-tunnel-down, 872, "IPSEC tunnel with peer 10.218.42.111 (routing-instance EXXON-Control-VR) is up", USPAB
2021-12-04T01:29:14.807814+00:00 USHCO-EXXON, ipsec-ike-down, 871, "IKE connection with peer 10.218.42.111 (routing-instance EXXON-Control-VR) is up", USPAB';
preg_match_all($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