$re = '/(?:[^,]*\,){9}(.*?)\,/';
$str = '<13>Apr 20 16:19:36 SERVERNAME.domain.net 1,2021/04/20 16:19:36,013244444796,THREAT,data,2049,2021/04/20 16:19:36,1.1.1.1,2.2.2.2,3.3.3.3,4.4.4.4,FWRULE NAME,,,sharepoint-online-uploading,vsys1,fwrulename,zone,protocol.stuff,ethernet1/1,SourceOS,2021/04/20 16:19:36,34916,1,49538,443,11070,443,0x1406000,tcp,alert,"\'FILE_01.docx\'",DataPattern-Conf(60004),computer-and-internet-info,low,client-to-server,69181231233089036,0xa000000000000000,100.0.0.0-100.255.255.255,United States,0,,0,,,3,,,,,,,,0,13,14,35,11,,SERVERNAME,,,,,0,,0,,N/A,unknown,AppThreat-0-0,0x0,0,424949495,';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($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