$re = '/(?<=")(.*)(?=")/m';
$str = '"https://gist.githubusercontent.com/anonymous/d2efee7b3967debc531d67de9cc7993a/raw/3f5e0e63ce6fe3aa4cffc2d0afafd2415408308a/gistfile1.txt"';
preg_match_all($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