简述php如何检测apache mod_rewrite模块是否安装

/**
 * @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(&#39;apache_get_modules&#39;))
  {
    $aMods = apache_get_modules();
    $bIsRewrite = in_array(&#39;mod_rewrite&#39;, $aMods);
  }
  else
  {
    $bIsRewrite = (strtolower(getenv(&#39;HTTP_MOD_REWRITE&#39;)) == &#39;on&#39;);
  }
  return $bIsRewrite;
}

if (!isRewriteMod()) exit('Please install Apache mod_rewrite module.');