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A Guide to The Rails Command Line

Rails comes with every command line tool you’ll need to

  • Create a Rails application
  • Generate models, controllers, database migrations, and unit tests
  • Start a development server
  • Experiment with objects through an interactive shell
  • Profile and benchmark your new creation


NOTE: This tutorial assumes you have basic Rails knowledge from reading the Getting Started with Rails Guide.

WARNING. This Guide is based on Rails 3.0. Some of the code shown here will not work in earlier versions of Rails.

Command Line Basics

There are a few commands that are absolutely critical to your everyday usage of Rails. In the order of how much you’ll probably use them are:

  • rails console
  • rails server
  • rake
  • rails generate
  • rails dbconsole
  • rails new app_name

Let’s create a simple Rails application to step through each of these commands in context.

rails new

The first thing we’ll want to do is create a new Rails application by running the rails new command after installing Rails.

WARNING: You can install the rails gem by typing gem install rails, if you don’t have it already. Follow the instructions in the Rails 3 Release Notes

$ rails new commandsapp
create README
create .gitignore
create Rakefile
create Gemfile
create app

create tmp/cache
create tmp/pids
create vendor/plugins
create vendor/plugins/.gitkeep

Rails will set you up with what seems like a huge amount of stuff for such a tiny command! You’ve got the entire Rails directory structure now with all the code you need to run our simple application right out of the box.

INFO: This output will seem very familiar when we get to the generate command. Creepy foreshadowing!

rails server

The rails server command launches a small web server named WEBrick which comes bundled with Ruby. You’ll use this any time you want to view your work through a web browser.

INFO: WEBrick isn’t your only option for serving Rails. We’ll get to that in a later section.

Without any prodding of any kind, rails server will run our new shiny Rails app:

$ cd commandsapp
$ rails server
=> Booting WEBrick
=> Rails 3.1.0 application starting in development on
=> Call with -d to detach
=> Ctrl-C to shutdown server
[2010-04-18 03:20:33] INFO WEBrick 1.3.1
[2010-04-18 03:20:33] INFO ruby 1.8.7 (2010-01-10) [x86_64-linux]
[2010-04-18 03:20:33] INFO WEBrick::HTTPServer#start: pid=26086 port=3000

With just three commands we whipped up a Rails server listening on port 3000. Go to your browser and open http://localhost:3000, you will see a basic Rails app running.

You can also use the alias “s” to start the server: rails s.

rails generate

The rails generate command uses templates to create a whole lot of things. You can always find out what’s available by running rails generate by itself. Let’s do that:

$ rails generate
Usage: rails generate generator [args] [options]

Please choose a generator below.


NOTE: You can install more generators through generator gems, portions of plugins you’ll undoubtedly install, and you can even create your own!

Using generators will save you a large amount of time by writing boilerplate code, code that is necessary for the app to work, but not necessary for you to spend time writing. That’s what we have computers for.

Let’s make our own controller with the controller generator. But what command should we use? Let’s ask the generator:

INFO: All Rails console utilities have help text. As with most *nix utilities, you can try adding —help or -h to the end, for example rails server —help.

$ rails generate controller
Usage: rails generate controller NAME [action action] [options]

rails generate controller CreditCard open debit credit close

Credit card controller with URLs like /credit_card/debit. Controller: app/controllers/credit_card_controller.rb Views: app/views/credit_card/debit.html.erb […] Helper: app/helpers/credit_card_helper.rb Test: test/functional/credit_card_controller_test.rb

Modules Example:
rails generate controller ‘admin/credit_card’ suspend late_fee

Credit card admin controller with URLs like /admin/credit_card/suspend. Controller: app/controllers/admin/credit_card_controller.rb Views: app/views/admin/credit_card/debit.html.erb […] Helper: app/helpers/admin/credit_card_helper.rb Test: test/functional/admin/credit_card_controller_test.rb

The controller generator is expecting parameters in the form of generate controller ControllerName action1 action2. Let’s make a Greetings controller with an action of hello, which will say something nice to us.

$ rails generate controller Greetings hello
create app/controllers/greetings_controller.rb
route get “greetings/hello”
invoke erb
create app/views/greetings
create app/views/greetings/hello.html.erb
invoke test_unit
create test/functional/greetings_controller_test.rb
invoke helper
create app/helpers/greetings_helper.rb
invoke test_unit
create test/unit/helpers/greetings_helper_test.rb
invoke assets
create app/assets/javascripts/greetings.js
create app/assets/stylesheets/greetings.css

What all did this generate? It made sure a bunch of directories were in our application, and created a controller file, a view file, a functional test file, a helper for the view, a javascript file and a stylesheet file.

Check out the controller and modify it a little (in app/controllers/greetings_controller.rb):

class GreetingsController < ApplicationController
def hello
@message = “Hello, how are you today?”

Then the view, to display our message (in app/views/greetings/hello.html.erb):

A Greeting for You!

<%= @message %>

Deal. Go check it out in your browser. Fire up your server using rails server.

$ rails server
=> Booting WEBrick…

WARNING: Make sure that you do not have any “tilde backup” files in app/views/(controller), or else WEBrick will not show the expected output. This seems to be a bug in Rails 2.3.0.

The URL will be http://localhost:3000/greetings/hello.

INFO: With a normal, plain-old Rails application, your URLs will generally follow the pattern of http://(host)/(controller)/(action), and a URL like http://(host)/(controller) will hit the index action of that controller.

Rails comes with a generator for data models too:

$ rails generate model
Usage: rails generate model NAME [field:type field:type] [options]

rails generate model account

Model: app/models/account.rb Test: test/unit/account_test.rb Fixtures: test/fixtures/accounts.yml Migration: db/migrate/XXX_add_accounts.rb rails generate model post title:string body:text published:boolean Creates a Post model with a string title, text body, and published flag.

NOTE: For a list of available field types, refer to the API documentation for the column method for the TableDefinition class.

But instead of generating a model directly (which we’ll be doing later), let’s set up a scaffold. A scaffold in Rails is a full set of model, database migration for that model, controller to manipulate it, views to view and manipulate the data, and a test suite for each of the above.

We will set up a simple resource called “HighScore” that will keep track of our highest score on video games we play.

$ rails generate scaffold HighScore game:string score:integer
exists app/models/
exists app/controllers/
exists app/helpers/
create app/views/high_scores
create app/views/layouts/
exists test/functional/
create test/unit/
create app/assets/stylesheets/
create app/views/high_scores/index.html.erb
create app/views/high_scores/show.html.erb
create app/views/high_scores/new.html.erb
create app/views/high_scores/edit.html.erb
create app/views/layouts/high_scores.html.erb
create app/assets/stylesheets/scaffold.css.scss
create app/controllers/high_scores_controller.rb
create test/functional/high_scores_controller_test.rb
create app/helpers/high_scores_helper.rb
route resources :high_scores
dependency model
exists app/models/
exists test/unit/
create test/fixtures/
create app/models/high_score.rb
create test/unit/high_score_test.rb
create test/fixtures/high_scores.yml
exists db/migrate
create db/migrate/20100209025147_create_high_scores.rb

The generator checks that there exist the directories for models, controllers, helpers, layouts, functional and unit tests, stylesheets, creates the views, controller, model and database migration for HighScore (creating the high_scores table and fields), takes care of the route for the resource, and new tests for everything.

The migration requires that we migrate, that is, run some Ruby code (living in that 20100209025147_create_high_scores.rb) to modify the schema of our database. Which database? The sqlite3 database that Rails will create for you when we run the rake db:migrate command. We’ll talk more about Rake in-depth in a little while.

$ rake db:migrate
(in /home/foobar/commandsapp)
== CreateHighScores: migrating ===========
— create_table(:high_scores)
→ 0.0026s
== CreateHighScores: migrated (0.0028s) ==========

INFO: Let’s talk about unit tests. Unit tests are code that tests and makes assertions about code. In unit testing, we take a little part of code, say a method of a model, and test its inputs and outputs. Unit tests are your friend. The sooner you make peace with the fact that your quality of life will drastically increase when you unit test your code, the better. Seriously. We’ll make one in a moment.

Let’s see the interface Rails created for us.

$ rails server

Go to your browser and open http://localhost:3000/high_scores, now we can create new high scores (55,160 on Space Invaders!)

rails console

The console command lets you interact with your Rails application from the command line. On the underside, rails console uses IRB, so if you’ve ever used it, you’ll be right at home. This is useful for testing out quick ideas with code and changing data server-side without touching the website.

You can also use the alias “c” to invoke the console: rails c.

If you wish to test out some code without changing any data, you can do that by invoking rails console —sandbox.

$ rails console —sandbox
Loading development environment in sandbox (Rails 3.1.0)
Any modifications you make will be rolled back on exit

rails dbconsole

rails dbconsole figures out which database you’re using and drops you into whichever command line interface you would use with it (and figures out the command line parameters to give to it, too!). It supports MySQL, PostgreSQL, SQLite and SQLite3.

You can also use the alias “db” to invoke the dbconsole: rails db.

rails plugin

The rails plugin command simplifies plugin management; think a miniature version of the Gem utility. Let’s walk through installing a plugin. You can call the sub-command discover, which sifts through repositories looking for plugins, or call source to add a specific repository of plugins, or you can specify the plugin location directly.

Let’s say you’re creating a website for a client who wants a small accounting system. Every event having to do with money must be logged, and must never be deleted. Wouldn’t it be great if we could override the behavior of a model to never actually take its record out of the database, but instead, just set a field?

There is such a thing! The plugin we’re installing is called acts_as_paranoid, and it lets models implement a deleted_at column that gets set when you call destroy. Later, when calling find, the plugin will tack on a database check to filter out “deleted” things.

$ rails plugin install

rails runner

runner runs Ruby code in the context of Rails non-interactively. For instance:

$ rails runner “Model.long_running_method”

rails destroy

Think of destroy as the opposite of generate. It’ll figure out what generate did, and undo it.

$ rails generate model Oops
exists app/models/
exists test/unit/
exists test/fixtures/
create app/models/oops.rb
create test/unit/oops_test.rb
create test/fixtures/oops.yml
exists db/migrate
create db/migrate/20081221040817_create_oops.rb
$ rails destroy model Oops
notempty db/migrate
notempty db
rm db/migrate/20081221040817_create_oops.rb
rm test/fixtures/oops.yml
rm test/unit/oops_test.rb
rm app/models/oops.rb
notempty test/fixtures
notempty test
notempty test/unit
notempty test
notempty app/models
notempty app


Rake is Ruby Make, a standalone Ruby utility that replaces the Unix utility ‘make’, and uses a ‘Rakefile’ and .rake files to build up a list of tasks. In Rails, Rake is used for common administration tasks, especially sophisticated ones that build off of each other.

You can get a list of Rake tasks available to you, which will often depend on your current directory, by typing rake —tasks. Each task has a description, and should help you find the thing you need.

$ rake —tasks
(in /home/foobar/commandsapp)
rake db:abort_if_pending_migrations # Raises an error if there are pending migrations
rake db:charset # Retrieves the charset for the current environment’s database
rake db:collation # Retrieves the collation for the current environment’s database
rake db:create # Create the database defined in config/database.yml for the current Rails.env

rake tmp:pids:clear # Clears all files in tmp/pids
rake tmp:sessions:clear # Clears all files in tmp/sessions
rake tmp:sockets:clear # Clears all files in tmp/sockets


rake about gives information about version numbers for Ruby, RubyGems, Rails, the Rails subcomponents, your application’s folder, the current Rails environment name, your app’s database adapter, and schema version. It is useful when you need to ask for help, check if a security patch might affect you, or when you need some stats for an existing Rails installation.

$ rake about
About your application’s environment
Ruby version 1.8.7 (x86_64-linux)
RubyGems version 1.3.6
Rack version 1.1
Rails version 3.1.0
Active Record version 3.1.0
Action Pack version 3.1.0
Active Resource version 3.1.0
Action Mailer version 3.1.0
Active Support version 3.1.0
Middleware ActionDispatch::Static, Rack::Lock, Rack::Runtime, Rails::Rack::Logger, ActionDispatch::ShowExceptions, ActionDispatch::RemoteIp, Rack::Sendfile, ActionDispatch::Callbacks, ActionDispatch::Cookies, ActionDispatch::Session::CookieStore, ActionDispatch::Flash, ActionDispatch::ParamsParser, Rack::MethodOverride, ActionDispatch::Head
Application root /home/foobar/commandsapp
Environment development


You can precompile the assets in app/assets using rake assets:precompile and remove compiled assets using rake assets:clean.


The most common tasks of the db: Rake namespace are migrate and create, and it will pay off to try out all of the migration rake tasks (up, down, redo, reset). rake db:version is useful when troubleshooting, telling you the current version of the database.


If you want to strip out or rebuild any of the Rails documentation (including this guide!), the doc: namespace has the tools. Stripping documentation is mainly useful for slimming your codebase, like if you’re writing a Rails application for an embedded platform.


These tasks will search through your code for commented lines beginning with “FIXME”, “OPTIMIZE”, “TODO”, or any custom annotation (like XXX) and show you them.


rake routes will list all of your defined routes, which is useful for tracking down routing problems in your app, or giving you a good overview of the URLs in an app you’re trying to get familiar with.


INFO: A good description of unit testing in Rails is given in A Guide to Testing Rails Applications

Rails comes with a test suite called Test::Unit. It is through the use of tests that Rails itself is so stable, and the slew of people working on Rails can prove that everything works as it should.

The test: namespace helps in running the different tests you will (hopefully!) write.


The Rails.root/tmp directory is, like the *nix /tmp directory, the holding place for temporary files like sessions (if you’re using a file store for files), process id files, and cached actions. The tmp: namespace tasks will help you clear them if you need to if they’ve become overgrown, or create them in case of deletions gone awry.


  • rake stats is great for looking at statistics on your code, displaying things like KLOCs (thousands of lines of code) and your code to test ratio.
  • rake secret will give you a pseudo-random key to use for your session secret.
  • rake time:zones:all lists all the timezones Rails knows about.

The Rails Advanced Command Line

More advanced use of the command line is focused around finding useful (even surprising at times) options in the utilities, and fitting those to your needs and specific work flow. Listed here are some tricks up Rails’ sleeve.

Rails with Databases and SCM

When creating a new Rails application, you have the option to specify what kind of database and what kind of source code management system your application is going to use. This will save you a few minutes, and certainly many keystrokes.

Let’s see what a —git option and a —database=postgresql option will do for us:

$ mkdir gitapp
$ cd gitapp
$ git init
Initialized empty Git repository in .git/
$ rails new . —git —database=postgresql
create app/controllers
create app/helpers

create tmp/cache
create tmp/pids
create Rakefile
add ‘Rakefile’
create README
add ‘README’
create app/controllers/application_controller.rb
add ‘app/controllers/application_controller.rb’
create app/helpers/application_helper.rb

create log/test.log
add ‘log/test.log’

We had to create the gitapp directory and initialize an empty git repository before Rails would add files it created to our repository. Let’s see what it put in our database configuration:

$ cat config/database.yml

  1. PostgreSQL. Versions 7.4 and 8.x are supported.
  2. Install the ruby-postgres driver:
  3. gem install ruby-postgres
  4. On Mac OS X:
  5. gem install ruby-postgres — —include=/usr/local/pgsql
  6. On Windows:
  7. gem install ruby-postgres
  8. Choose the win32 build.
  9. Install PostgreSQL and put its /bin directory on your path.
    adapter: postgresql
    encoding: unicode
    database: gitapp_development
    pool: 5
    username: gitapp

It also generated some lines in our database.yml configuration corresponding to our choice of PostgreSQL for database. The only catch with using the SCM options is that you have to make your application’s directory first, then initialize your SCM, then you can run the rails new command to generate the basis of your app.

server with Different Backends

Many people have created a large number different web servers in Ruby, and many of them can be used to run Rails. Since version 2.3, Rails uses Rack to serve its webpages, which means that any webserver that implements a Rack handler can be used. This includes WEBrick, Mongrel, Thin, and Phusion Passenger (to name a few!).

NOTE: For more details on the Rack integration, see Rails on Rack.

To use a different server, just install its gem, then use its name for the first parameter to rails server:

$ sudo gem install mongrel
Building native extensions. This could take a while…
Building native extensions. This could take a while…
Successfully installed gem_plugin-0.2.3
Successfully installed fastthread-1.0.1
Successfully installed cgi_multipart_eof_fix-2.5.0
Successfully installed mongrel-1.1.5

Installing RDoc documentation for mongrel-1.1.5…
$ rails server mongrel
=> Booting Mongrel (use ‘rails server webrick’ to force WEBrick)
=> Rails 3.1.0 application starting on

The Rails Generation: Generators

INFO: For a good rundown on generators, see Understanding Generators. A lot of its material is presented here.

Generators are code that generates code. Let’s experiment by building one. Our generator will generate a text file.

The Rails generator by default looks in these places for available generators, where Rails.root is the root of your Rails application, like /home/foobar/commandsapp:

  • Rails.root/lib/generators
  • Rails.root/vendor/generators
  • Inside any plugin with a directory like “generators” or “rails_generators”
  • ~/.rails/generators
  • Inside any Gem you have installed with a name ending in “_generator”
  • Inside any Gem installed with a “rails_generators” path, and a file ending in “_generator.rb”
  • Finally, the builtin Rails generators (controller, model, mailer, etc.)

Let’s try the fourth option (in our home directory), which will be easy to clean up later:

$ mkdir -p ~/.rails/generators/tutorial_test/templates
$ touch ~/.rails/generators/tutorial_test/templates/tutorial.erb
$ touch ~/.rails/generators/tutorial_test/tutorial_test_generator.rb

We’ll fill tutorial_test_generator.rb out with:

class TutorialTestGenerator < Rails::Generator::Base
def initialize(runtime_args)
@tut_args = runtime_args

def manifest record do |m| “public” m.template “tutorial.erb”, File.join(“public”, “tutorial.txt”), :assigns => { :args => @tut_args } end end


We take whatever args are supplied, save them to an instance variable, and literally copying from the Rails source, implement a manifest method, which calls record with a block, and we:

  • Check there’s a public directory. You bet there is.
  • Run the ERB template called “tutorial.erb”.
  • Save it into “Rails.root/public/tutorial.txt”.
  • Pass in the arguments we saved through the :assigns parameter.

Next we’ll build the template:

$ cat ~/.rails/generators/tutorial_test/templates/tutorial.erb
I’m a template!

I got assigned some args:
<%= require ‘pp’; PP.pp(args, "") %>

Then we’ll make sure it got included in the list of available generators:

$ rails generate

Installed Generators
User: tutorial_test

SWEET! Now let’s generate some text, yeah!

$ rails generate tutorial_test arg1 arg2 arg3
exists public
create public/tutorial.txt

And the result:

$ cat public/tutorial.txt
I’m a template!

I got assigned some args:
[[“arg1”, “arg2”, “arg3”],


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