Something like Hubot, implemented on top of Botkit

bot.js

require('dotenv').config()

var Fs = require('fs')
var Path = require('path')
var Botkit = require('botkit')

if (!process.env.SLACK_TOKEN) {
  console.error('ERROR: this requires "SLACK_TOKEN" to be a valid Slack API token.')
  process.exit(-1)
}

var controller = Botkit.slackbot({
  debug: false
})

controller.spawn({
  token: process.env.SLACK_TOKEN
}).startRTM()

controller.hears('ping', 'direct_message', function (bot, msg) {
  bot.reply(msg, 'PONG')
})

controller.hears(['help ?(.*)'], ['direct_message', 'direct_mention', 'mention'], function (bot,msg) {
  bot.startTyping(msg)
  var results = []
  var re = RegExp(msg.match[1], 'gi')
  for (var i in helpEntries) {
    he = helpEntries[i]
    if (he.search(re) != -1) results.push(he)
  }
  bot.reply(msg, results.join('\n'))
})

// Load scripts
var helpEntries = []
var scriptDir = Path.resolve('.', 'scripts')
var scripts = Fs.readdirSync(scriptDir).sort()
for (var i in scripts) {
  var file = scripts[i]
  var ext = Path.extname(file)
  var path = Path.join(scriptDir, Path.basename(file, ext))
  if (!require.extensions[ext]) continue
  
  var script
  try {
    controller.log('Loading script:', file)
    script = require(path)
    
    // Call init function so script can set up listeners
    if (typeof(script.init) === 'function') {
      script.init(controller)
    } else {
      controller.log.error('expected init to be a function, instead was ' + typeof(script.init))
    }
    
    // Put the help items into the help directory
    if (script.help) {
      helpEntries = helpEntries.concat(script.help)
    }
  } catch (e) {
    controller.log.error("Couldn't load", file, '\n', e)
  }
}

pug.js

// Put this in the "scripts" directory

var request = require('request')
var _ = require('underscore')

function getRandomInt(min, max) {
  return Math.floor(Math.random() * (max - min)) + min;
}

function fetchResults(bot, msg, n, cb) {
  request({
    url: 'https://api.datamarket.azure.com/Bing/Search/Image',
    qs: {
      Query: "'cute pug'",
      $skip: getRandomInt(0, 100),
      $top: n,
      $format: 'json'
    },
    auth: {
      user: process.env.BING_ACCOUNT_KEY || null,
      pass: process.env.BING_ACCOUNT_KEY || null
    }
  }, function(err, res, body) {
    if (err || (res && res.statusCode !== 200)) {
      bot.reply(msg, "Whoops, got an error: " + err + ' ' + 
        res.statusCode + ' ' + res.statusMessage)
    } else {
      cb(JSON.parse(body).d.results)
    }
  })
}

module.exports = {
  init: function (controller) {
    if (!process.env.BING_ACCOUNT_KEY) {
      controller.log.warning('To enable pug commands, provide BING_ACCOUNT_KEY')
      return
    }
    
    contexts = ['direct_message', 'direct_mention', 'mention']

    controller.hears('pug bomb ?(.*)?', contexts, function (bot,msg) {
      bot.startTyping(msg)
      fetchResults(bot, msg, msg.match[1] || 10, function (results) {
        _.each(results, function (result) {
          bot.reply(msg, result.MediaUrl)
        })
      })
    })

    controller.hears('pug( me)?', contexts, function (bot,msg) {
      bot.startTyping(msg)
      fetchResults(bot, msg, 1, function (results) {
        bot.reply(msg, results[0].MediaUrl)
      })
    })
  },
  help: [
    'pug [me] - Get a pug',
    'pug bomb [N] - Get N pugs (default 10)'
  ]
}