php检测apache mod_rewrite模块是否安装的方法

/**
 * @title check if apache's mod_rewrite is installed.
 * 
 * @author pierre-henry soria <ph7software@gmail.com>
 * @copyright (c) 2013, pierre-henry soria. all rights reserved.
 * @return boolean
 */
function isrewritemod()
{
  if (function_exists('apache_get_modules'))
  {
    $amods = apache_get_modules();
    $bisrewrite = in_array('mod_rewrite', $amods);
  }
  else
  {
    $bisrewrite = (strtolower(getenv('http_mod_rewrite')) == 'on');
  }
  return $bisrewrite;
}

if (!isrewritemod()) exit('please install apache mod_rewrite module.');