Gemfile

# Relevant bits of Gemfile...
group :development do
  gem 'guard'
  gem 'listen', :github => 'guard/listen'
  gem 'celluloid-io'
end

guard

#!bin/bash
# My computer uses eth2 instead of eth0 for some bizzare ass reason,
#  you'll probably need to change it to get the correct IP
IP=$(ifconfig eth2 | sed -n "2s/[^:]*:[ \t]*\([^ ]*\) .*/\1/p")

trap "kill 0" SIGINT SIGTERM EXIT

listen -r -f 0.0.0.0:4000 &
docker-compose run dev bundle exec guard -o $IP:4000

Guardfile

guard :rspec, cmd: 'rspec' do

  watch(%r{spec/(.+)_spec.rb$}) { |m| "spec/#{m[1]}_spec.rb" }
  watch(%r{lib/(.+).rb$})     { |m| "spec/lib/#{m[1]}_spec.rb" }
  watch('spec/spec_helper.rb')  { "spec" }

  watch(%r{app/(.+).rb$})                           { |m| "spec/#{m[1]}_spec.rb" }
  watch(%r{app/(.*)(.erb|.haml)$})                 { |m| "spec/#{m[1]}#{m[2]}_spec.rb" }
  watch(%r{app/controllers/(.+)_(controller).rb$})  { |m| ["spec/routing/#{m[1]}_routing_spec.rb", "spec/#{m[2]}s/#{m[1]}_#{m[2]}_spec.rb", "spec/acceptance/#{m[1]}_spec.rb"] }
  watch(%r{spec/support/(.+).rb$})                  { "spec" }
  watch('config/routes.rb')                           { "spec/routing" }
  watch('app/controllers/application_controller.rb')  { "spec/controllers" }

end