)#i", create_function('$matches', 'return fixLink($matches[1]);'), $str); } // receives a string that contains a link such as // and adds the ref="nofollow" attribute if the domain isn't in the white list function fixLink($input) { // retrieve the whitelist from the config file $whitelist = $GLOBALS['whitelist']; // if the link in $input already contains ref="nofollow", return it as it is if (preg_match('#rel\s*?=\s*?[\'"]?.*?nofollow.*?[\'"]?#i', $input)) { return $input; } // extract the URL from $input preg_match('#href\s*?=\s*?[\'"]?([^\'"]*)[\'"]?#i', $input, $captures); // $href will contain the extracted URL, such as http://seophp.example.com $href = $captures[1]; // if URL doesn't contain http://, assume it's a local link if (!preg_match('#^\s*http://#', $href)) { return $input; } // extract the host name of the URL, such as seophp.example.com $parsed = parse_url($href); $host = $parsed['host']; // if the URL is in the whitelist, send $input back as it is if (in_array($host, $whitelist)) { return $input; } // assuming the URL already has a rel attribute, change its value to nofollow $x = preg_replace('#(rel\s*=\s*([\'"]?))((?(3)[^\'"]*|[^\'" ]*))([\'"]?)#i', '\\1\\3,nofollow\\4', $input); // if the string has been modified, it means it already had a rel attribute, // whose value has been changed to nofollow, so we return the new version if ($x != $input) { return $x; } // if the link in the input string doesn't have ref attribute, we add it else { return preg_replace('#