app.rb

# To enable files to be served from "./public/", the :static
# and :app_file options have to be set.

require 'rubygems'
require 'sinatra/base'

class App < Sinatra::Base
  set :static, true
  set :app_file, __FILE__

  get '/' do
    'See <a href="/thing.txt">this text file</a>.'
  end
end

config.ru

require 'app'
run App

run.sh

#!/bin/sh

thin start -R config.ru

standalone.rb

# This standalone version can serve the text file just fine

require 'rubygems'
require 'sinatra'

get '/' do
  'See <a href="/thing.txt">this text file</a>.'
end

thing.txt

How do I get this file served automatically?