$re = '/\G\s*+((\((?:\s*+(?2)\s*+(?(?!\)),)|\s*+[^()\',\s]++\s*+(?(?!\)),)|\s*+\'[^\'\r\n]*+\'\s*+(?(?!\)),))++\))|[^()\',\s]++|\'[^\'\r\n]*+\')\s*+(?:,|$)/';
$str = '65.54.188.59 - - [13/Jul/2005:04:10:13 +0200] "GET /fusel/Suchmaschinen.html HTTP/1.0" 404 302 "-" "msnbot/1.0 (+http://search.msn.com/msnbot.htm)"';
$subst = "\n";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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