$re = '/\{\"line\":\"(?<time>.+)\|(?<log_level>.+)\|(?<Controller>.+)\|(?<Message>.+\}|.+?)\"/m';
$str = '{"line":"18:48:17.990|INFO|PController|Plex event is media.pause}","source":"stdout","tag":"4e263fa2001d"}
{"line":"22:38:47.839|INFO|PController|{\\"Id\\":\\"SMf1bc2466b1\\",\\"ErrorMessages\\":null}","source":"stdout","tag":"b5fcd8b8b5a4"}
{"line":"22:38:47.839|INFO|PController|This is another test","source":"stdout","tag":"b5fcd8b8b5a4"}
{"line":"18:56:37.212|INFO|PController|media.stop","source":"stdout","tag":"4e263fa2001d"}';
preg_match_all($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