application.rb

require 'lib/caching'

get '/' do
  cache(erb(:index, :layout => :main))
end

cache_sweeper.rb

#! /usr/bin/env ruby
#
# This script is to be run via cron while with the cwd in the 
# Sinatra root directory. 
#

require 'fileutils'

TWENTY_FOUR_HOURS = 60*60*24

Dir['public/*.html'].each do |path|
  mtime = File.mtime(path)
  
  if (mtime.to_i + TWENTY_FOUR_HOURS) < Time.now.to_i
    FileUtils.remove_file(path)
  end
end

caching.rb

require 'fileutils'

helpers do

  def cache(text)
   # requests to / should be cached as index.html
   uri = request.env["REQUEST_URI"] == "/" ? 'index' : request.env["REQUEST_URI"]

   # Don't cache pages with query strings.
   unless uri =~ /\?/
      uri << '.html'
      # put all cached files in public/
      path = File.join(File.dirname(__FILE__), '..', 'public', uri)

      # Write the text passed to the path
      File.open(path, 'w') { |f| f.write( text ) }
    end
    return text
  end

end