Download and Zip your slack emoji

dlemoji.rb

# gem install slack-ruby-client rubyzip
# run with: ruby dlemoji.rb

require 'rubygems'
require 'zip'
require 'slack-ruby-client'
require 'open-uri'

token = 'your slack api token'
directory = '/<absolute/path/to>/emoji/' # The emoji directory must exist, and be empty.
zipfile_name = 'emoji.zip'

# Download the image from slack's server and save locally 
def download_image(url, dest, dir = '')
  open(url) do |u|
    File.open(dir + dest, 'wb') { |f| f.write(u.read) }
  end
end

Slack.configure do |config|
  config.token = token
end

client = Slack::Web::Client.new

client.emoji_list.emoji.each do |name, url|
  next if url.include? 'alias:' # skip aliased emoji

  download_image(url, name + '.' + url.split('.').last, directory)
end

Zip::File.open(zipfile_name, Zip::File::CREATE) do |zipfile|
  Dir[File.join(directory, '*')].each do |file|
    zipfile.add(file.sub(directory, ''), file)
  end
end