sinatra boilerplate ref: http://qiita.com/hiroshi3110/items/aeae1f6c01cde0547f84

app.rb

get '/' do
  if @something_goes_wrong
    halt 400, "oops"
  end
  'hello world'
end

config.ru

require 'bundler'
Bundler.require
$stdout.sync = true # https://devcenter.heroku.com/articles/getting-started-with-ruby#logging               
require './app'
run Sinatra::Application

file3.txt

git init
git add app.rb config.ru Gemfile Gemfile.lock
git commit -m 'initial commit'
heroku create your-app-name
git push heroku master
heroku open

Gemfile

source "https://rubygems.org"
gem "sinatra"