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Rails Application Templates

Application templates are simple Ruby files containing DSL for adding gems/initializers etc. to your freshly created Rails project or an existing Rails project.

By referring to this guide, you will be able to:

  • Use templates to generate/customize Rails applications
  • Write your own reusable application templates using the Rails template API


To apply a template, you need to provide the Rails generator with the location of the template you wish to apply, using -m option. This can either be path to a file or a URL.

$ rails new blog -m ~/template.rb
$ rails new blog -m

You can use the rake task rails:template to apply templates to an existing Rails application. The location of the template needs to be passed in to an environment variable named LOCATION. Again, this can either be path to a file or a URL.

$ rake rails:template LOCATION=~/template.rb
$ rake rails:template LOCATION=

Template API

Rails templates API is very self explanatory and easy to understand. Here's an example of a typical Rails template:

# template.rb
run "rm public/index.html"
generate(:scaffold, "person name:string")
route "root to: 'people#index'"

git :init
git add: "."
git commit: %Q{ -m 'Initial commit' }

The following sections outlines the primary methods provided by the API:


Adds a gem entry for the supplied gem to the generated application’s Gemfile.

For example, if your application depends on the gems bj and nokogiri:

gem "bj"
gem "nokogiri"

Please note that this will NOT install the gems for you and you will have to run bundle install to do that.

bundle install

gem_group(*names, &block)

Wraps gem entries inside a group.

For example, if you want to load rspec-rails only in development and test group:

gem_group :development, :test do
  gem "rspec-rails"

add_source(source, options = {})

Adds the given source to the generated application's Gemfile.

For example, if you need to source a gem from "":

add_source ""

environment/application(data=nil, options={}, &block)

Adds a line inside the Application class for config/application.rb.

If options[:env] is specified, the line is appended to the corresponding file in config/environments.

environment 'config.action_mailer.default_url_options = {host: ''}, env: 'production'

A block can be used in place of the data argument.

vendor/lib/file/initializer(filename, data = nil, &block)

Adds an initializer to the generated application’s config/initializers directory.

Lets say you like using Object#not_nil? and Object#not_blank?:

initializer 'bloatlol.rb', <<-CODE
  class Object
    def not_nil?

    def not_blank?

Similarly lib() creates a file in the lib/ directory and vendor() creates a file in the vendor/ directory.

There is even file(), which accepts a relative path from Rails.root and creates all the directories/file needed:

file 'app/components/foo.rb', <<-CODE
  class Foo

That’ll create app/components directory and put foo.rb in there.

rakefile(filename, data = nil, &block)

Creates a new rake file under lib/tasks with the supplied tasks:

rakefile("bootstrap.rake") do
    namespace :boot do
      task :strap do
        puts "i like boots!"

The above creates lib/tasks/bootstrap.rake with a boot:strap rake task.

generate(what, *args)

Runs the supplied rails generator with given arguments.

generate(:scaffold, "person", "name:string", "address:text", "age:number")


Executes an arbitrary command. Just like the backticks. Let's say you want to remove the public/index.html file:

run "rm public/index.html"

rake(command, options = {})

Runs the supplied rake tasks in the Rails application. Let's say you want to migrate the database:

rake "db:migrate"

You can also run rake tasks with a different Rails environment:

rake "db:migrate", env: 'production'


Adds a routing entry to the config/routes.rb file. In above steps, we generated a person scaffold and also removed public/index.html. Now to make PeopleController#index as the default page for the application:

route "root to: 'person#index'"


Enables you to run a command from the given directory. For example, if you have a copy of edge rails that you wish to symlink from your new apps, you can do this:

inside('vendor') do
  run "ln -s ~/commit-rails/rails rails"


ask() gives you a chance to get some feedback from the user and use it in your templates. Lets say you want your user to name the new shiny library you’re adding:

lib_name = ask("What do you want to call the shiny library ?")
lib_name << ".rb" unless lib_name.index(".rb")

lib lib_name, <<-CODE
  class Shiny

yes?(question) or no?(question)

These methods let you ask questions from templates and decide the flow based on the user’s answer. Lets say you want to freeze rails only if the user want to:

rake("rails:freeze:gems") if yes?("Freeze rails gems?")
# no?(question) acts just the opposite.


Rails templates let you run any git command:

git :init
git add: "."
git commit: "-a -m 'Initial commit'"
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