PHP methods for directory operations

/**
 * Calculate the full size of a directory
 *
 * @author   Jonas John
 * @version   0.2
 * @param    string  $DirectoryPath  Directory path
 */
function CalcDirectorySize($DirectoryPath) {
  // I reccomend using a normalize_path function here
  // to make sure $DirectoryPath contains an ending slash
  // To display a good looking size you can use a readable_filesize
  // function.
  $Size = 0;
  $Dir = opendir($DirectoryPath);
  if (!$Dir)
    return -1;
  while (($File = readdir($Dir)) !== false) {
    // Skip file pointers
    if ($File[0] == '.') continue; 
    // Go recursive down, or add the file size
    if (is_dir($DirectoryPath . $File))      
      $Size += CalcDirectorySize($DirectoryPath . $File . DIRECTORY_SEPARATOR);
    else 
      $Size += filesize($DirectoryPath . $File);    
  }
  closedir($Dir);
  return $Size;
}
//使用范例：
$SizeInBytes = CalcDirectorySize('data/');