http://stephencelis.com/2009/04/18/yaac-yes-yet-another.html

app_template.rb

# App (http://github.com/stephencelis/app), a template for Rails:
#
# In existing projects:
#   % rake rails:template LOCATION=http://gist.github.com/97629.txt
#
# For new projects:
#   % rails newapp -m http://gist.github.com/97629.txt

unless File.read("config/environment.rb").include? "stephencelis-app"
  gem "stephencelis-app", :lib     => "app",
                          :source  => "http://gems.github.com",
                          :version => ">= 0.2.2"
end

unless File.exist? "config/app.yml"
  generate "app_config"
end

begin
  Gem.activate "stephencelis-app"
rescue Gem::LoadError
  rake "gems:install", :sudo => true
end

unless Dir["vendor/gems/stephencelis-app*"].any?
  if File.directory?("vendor/gems") && yes?("Unpack gem?")
    rake "gems:unpack", :sudo => true
  end
end