function delFile($dir, $fileName)
 {
     if ($fileName == "all") {
         $dirUtil = new DirUtil();
         $fileList = $dirUtil->traverse($dir);
         foreach ($fileList as $f) {
             if (!unlink("{$dir}/{$f}")) {
                 echo "false";
                 exit;
             }
         }
         echo "true";
     } else {
         $ret = unlink("{$dir}/{$fileName}");
         if ($ret) {
             echo "true";
         } else {
             echo "false";
         }
     }
 }