$re = '/Session: (.+?)[\n;]/';
$str = 'RTSP/1.0 200 OK
CSeq: 3
Server: Ants Rtsp Server/1.0
Date: 21 Oct 2016 15:55:30 GMT
Session: 980603187; timeout=60
Transport: RTP/AVP/TCP;unicast;interleaved=0-1;ssrc=F006B800
RTSP/1.0 200 OK
CSeq: 3
Server: Ants Rtsp Server/1.0
Date: 21 Oct 2016 15:55:30 GMT
Session: 980603187
Transport: RTP/AVP/TCP;unicast;interleaved=0-1;ssrc=F006B800';
preg_match_all($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