code: function tail (argv, callback) {
    if (!argv[2]) {
      console.error('url is required')
      console.error('Usage : tail <url>')
      process.exit(-1)
    }
    var uri = argv[2]
    var wss = 'wss://' + uri.split('/')[2] + '/'
  
    var s = new ws(wss, {
      origin: 'http://websocket.org'
    })
  
    s.on('open', function open () {
      s.send('sub ' + uri)
    })
  
    s.on('close', function close () {
      console.log('disconnected')
    })
  
    s.on('message', function message (data, flags) {
      var a = data.split(' ')
      if (a.length && a[0] === 'pub') {
        util.get(a[1], function (err, res) {
          if (err) {
            console.error('Error : ' + err)
          } else {
            console.log(res)
          }
        })
      }
    })
  }
docs: tail gets list of files for a given container
  
  @param {String} argv[2] url
  @callback {bin~cb} callback