$re = '/(?<=\s)[0-9a-f]{2}(:[0-9a-f]{2}){5}\s+-?[[:digit:]]{2}/m';
$str = ' SSID BSSID RSSI CHANNEL
Something 12:34:56:78:98:ab -10 1
Something guest a2:34:56:78:98:ab -10 2
Network b2:34:56:78:98:ab -20 3
Public network c2:34:56:78:98:ab -30 4';
preg_match_all($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