PHP batch conversion method for encoding all files in a folder

<?php
/**
 * 把一个文件夹里的文件全部转码 只能转一次 否则全部变乱码
 * @param string $filename
 */
function iconv_file($filename,$input_encoding=&#39;gbk&#39;,$output_encoding=&#39;utf-8&#39;)
{
  if(file_exists($filename))
  {
    if(is_dir($filename))
    {
      foreach (glob("$filename/*") as $key=>$value)
      {
        iconv_file($value);
      }
    }
    else
    {
      $contents_before = file_get_contents($filename);
      /*$encoding = mb_detect_encoding($contents_before,array(&#39;CP936&#39;,&#39;ASCII&#39;,&#39;GBK&#39;,&#39;GB2312&#39;,&#39;UTF-8&#39;));
      echo $encoding;
      if($encoding==&#39;UTF-8&#39;) mb_detect_encoding函数不工作
      {
        return;
      }*/
      $contents_after = iconv($input_encoding,$output_encoding,$contents_before);
      file_put_contents($filename, $contents_after);
    }
  }
  else
  {
    echo &#39;参数错误&#39;;
    return false;
  }
}
iconv_file(&#39;./test&#39;);
?>