A Rake task for precompiling assets in a Sinatra app using Sprockets.

Gemfile

source 'http://rubygems.org'

# app base
gem 'logger'
gem 'rack'
gem 'sinatra'
gem 'sinatra-assetpack'
gem 'sprockets'
gem 'sprockets-helpers'

# css, js, and js templates
gem 'sass'
gem 'coffee-script'
gem 'uglifier'
gem 'ejs'

Rakefile

require 'rubygems'
require 'bundler'

Bundler.require

# Configure the base application.
# By default this uses SASS for css compression
# and Uglifier for Javascript compression.
#
# A standard directory structure is assumed:
#   /app
#     /assets
#       /images
#       /javascripts
#       /stylesheets
#   /public
#     /assets
#   /vendor
#     /assets
#       /fonts
#       /images
#       /javascripts
#       /stylesheets
class Application < Sinatra::Application

  set :root, Rake.original_dir
  set :sprockets, (Sprockets::Environment.new(root) { |env| env.logger = Logger.new(STDOUT) })
  set :assets_prefix, 'assets'
  set :assets_path, File.join(root, 'public', assets_prefix)

  configure do
    set :digest_assets,   true
    set :manifest_assets, true

    sprockets.append_path root+'/app/assets/images'
    sprockets.append_path root+'/app/assets/javascripts'
    sprockets.append_path root+'/app/assets/stylesheets'
    sprockets.append_path root+'/vendor/assets/fonts'
    sprockets.append_path root+'/vendor/assets/images'
    sprockets.append_path root+'/vendor/assets/javascripts'
    sprockets.append_path root+'/vendor/assets/stylesheets'

    sprockets.css_compressor = :scss
    sprockets.js_compressor  = Uglifier.new :mangle => false
  end

end

# Each task uses the configured app
namespace :assets do

  desc 'precompile all assets'
  task :precompile => [:clean] do
    puts 'precompiling assets'
    path        = Application.settings.assets_path
    sprockets   = Application.settings.sprockets
    manifest    = Sprockets::Manifest.new sprockets, path
    comp_filter = /application.(js|coffee|css|sass|scss)/
    copy_filter = /(.otf|.woff|.ttf|.svg|.eot|.png|.ico|.gif|.bmp|.jpg)/
    assets      = []

    sprockets.each_logical_path do |p|
      assets.push p if p.match comp_filter
      sprockets[p].write_to "#{path}/#{p}" if p.match copy_filter
    end

    manifest.compile assets
  end

  desc 'cleanup old assets and leave only the currently active precompiled set'
  task :clean do
    puts 'cleaning up old assets'
    sprockets = Application.settings.sprockets
    manifest  = Sprockets::Manifest.new sprockets, Application.settings.assets_path
    manifest.clean 1
  end

  desc 'delete all precompiled assets--not recommended in production'
  task :clobber do
    puts 'deleting all precompiled assets'
    sprockets = Application.settings.sprockets
    manifest  = Sprockets::Manifest.new sprockets, Application.settings.assets_path
    manifest.clobber
  end
end