code: function () {
      scan_mode = false;
      log.i('Now start qiniu watch.'.yellow);
      var watcher = chokidar.watch(local_dir, {ignored: /[\/\\]\./, persistent: true});
     
      watcher.on('add', function(file, event) {
          
          var name = path.join(dirPrefix, file.replace(local_dir, '')).replace(/\\/g, '/').replace(/^\//g, '');
          check_upload(file, name);
      });
     
      watcher.on('change', function(file, event) {
          
          var name2 = path.join(dirPrefix, file.replace(local_dir, '')).replace(/\\/g, '/').replace(/^\//g, '');
          check_upload(file, name2);
      });
  }
docs: 文件系统监听
  只监听添加文件和文件修改
  其中在每次监听初始化时，遍历到的文件都会触发添加文件事件