function getKeywords() {
  // 搜索引擎关键字映射
  static $host_keyword_map = array(
      'www.baidu.com' => 'wd',
      'v.baidu.com' => 'word',
      'image.baidu.com' => 'word',
      'news.baidu.com' => 'word',
      'www.so.com' => 'q',
      'video.so.com' => 'q',
      'image.so.com' => 'q',
      'news.so.com' => 'q',
      'www.sogou.com' => 'query',
      'pic.sogou.com' => 'query',
      'v.sogou.com' => 'query',
  );
  // 检查来源是否搜索引擎
  if (!isset($_SERVER['HTTP_REFERER'])) {
    return '';
  }
  $urls = parse_url($_SERVER['HTTP_REFERER']);
  if (!array_key_exists($urls['host'], $host_keyword_map)) {
    return '';
  }
  $key = $host_keyword_map[$urls['host']];
  // 检查关键字参数是否存在
  if (!isset($urls['query'])) {
    return '';
  }
  $params = array();
  parse_str($urls['query'], $params);
  if (!isset($params[$key])) {
    return '';
  }
  $keywords = $params[$key];
  // 检查编码
  $encoding = mb_detect_encoding($keywords, 'utf-8,gbk');
  if ($encoding != 'utf-8') {
    $keywords = iconv($encoding, 'utf-8', $keywords);
  }
  return $keywords;
}

<"Content-Type: text/html; charset=utf-8");
$referers = array(
    'http://www.baidu.com/s"\n";
}