$re = '/\"id\":\"(?<id>[^\"]+)\",\"category\":\"(?<category>[^\"]+)\",\"correlationId\":(?<correlationId>[^\"]+),\"activityDateTime\":\"(?<activityDateTime>[^\"]+)/m';
$str = '{"@odata.context":"https://graph.microsoft.com/v1.0/$metadata#auditLogs/directoryAudits","value":[]}
{"@odata.context":"https://graph.microsoft.com/v1.0/$metadata#auditLogs/directoryAudits","value":[]}
{"@odata.context":"https://graph.microsoft.com/v1.0/$metadata#auditLogs/directoryAudits","value":[{"id":"B2Cxx","category":"xxx","correlationId":xxx,"activityDateTime":"xxx"....},{"id":"B2Cxx","category":"xxx","correlationId":xxx,"activityDateTime":"xxx"....},{"id":"B2Cxx","category":"xxx","correlationId":xxx,"activityDateTime":"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