Please see part 1 of this post for the original implementation that includes the Gemfile, config.ru and Apache vhosts configuration...

app.rb

require 'open3'

WORKSPACE = '/var/www/deploy/whatevs_repo_clone'

post '/deploy' do
  begin
    write_log "Received post: branch #{data["branch_name"]} #{data["result"]}"

    if master_branch_passed?
      message_campfire deploy_notification, room
      deploy
    else
      write_log "SKIPPING DEPLOYMENT FOR #{data['branch_name']} with a result of #{data['result']}"
    end
  rescue => e
    write_log e.inspect
  end
end

get '/' do
  "Whatchu talkin bout, Willis?"
end

def write_log(log_message, filename = :master)
  File.open("log/deploy_#{filename.to_s}.log", "a") do |file|
    file.write "[#{current_time}] #{log_message.to_s}\n"
  end
end

def current_time
  Time.now.strftime("%Y-%m-%d %h:%m:%s")
end

def message_campfire(message, room)
  write_log "Messaged Campfire: #{message}"
  room.speak message
end

def campfire
  @campfire ||= Tinder::Campfire.new account, :token => token, :ssl_verify => false
end

def account
  ENV['CAMPFIRE_ACCOUNT']
end

def token
  ENV['CAMPFIRE_TOKEN']
end

def room
  @room ||= campfire.find_room_by_name("Whatevs")
end

def json
  request.body.read
end

def data
  @data ||= Yajl::Parser.parse(json)
end

def deploy_notification
  "Deploying #{data['branch_name']} to staging"
end

def master_branch_passed?
  data['branch_name'] == 'master' && data['result'] == 'passed'
end

def command
  @command ||= [
    "cd #{WORKSPACE}",
    "git reset --hard origin",
    "git pull origin master",
    "bundle install",
    "bundle exec cap staging deploy:migrations",
  ].join(" && ")
end

def deploy
  Bundler.with_sparkling_clean_env do
    write_log "Executing: #{command}"
    executed = Open3.capture3(command)
    write_log "stdout: #{executed[0]}"
    write_log "stderr: #{executed[1]}"
    write_log "success?: #{executed[2].success?}"
  end
  room.speak "Deployment finished: #{command}"
  write_log "DONE"
end

module Bundler
  class << self
    def with_sparkling_clean_env
      oenv = ENV.to_hash

      %w{BUNDLE_GEMFILE RUBYOPT GEM_HOME GIT_DIR GIT_WORK_TREE}.each { |key| ENV.delete(key) }

      yield

      ENV.replace(oenv)
    end
  end
end

For more UNIX tips, please check out
Learning the UNIX Command Line.

Enjoy,
Chip