$re = '/(https?[^\s?]+\?)([^\s=]+=[^\s&]+)(?:\&([^\s=]+=[^\s&]+))?(?:\&([^\s=]+=[^\s&]+))?(?:\&([^\s=]+=[^\s&]+))?/';
$str = 'https://github.com/search?utf8=%E2%9C%93&q=regex%20play&type=Repositories&ref=searchresults
https://github.com/search?utf8=%E2%9C%93&q=regex+play&type=Repositories&ref=searchresults&o=desc&s=updated
';
$subst = " \1\2&\3&\4&\5&o=desc&s=updated";
$result = preg_replace($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