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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
  • Mess 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.


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:

  • console
  • server
  • rake
  • generate
  • rails

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


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

WARNING: You know you need the rails gem installed by typing gem install rails first, right? Okay, okay, just making sure.

$ rails commandsapp

create create app/controllers create app/helpers create app/models … … create log/production.log create log/development.log create log/test.log

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!


Let’s try it! The 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, server will run our new shiny Rails app:

$ cd commandsapp
$ ./script/server
=> Booting WEBrick…
=> Rails 2.2.0 application started on
=> Ctrl-C to shutdown server; call with —help for options
[2008-11-04 10:11:38] INFO WEBrick 1.3.1
[2008-11-04 10:11:38] INFO ruby 1.8.5 (2006-12-04) [i486-linux]
[2008-11-04 10:11:38] INFO WEBrick::HTTPServer#start: pid=18994 port=3000

WHOA. With just three commands we whipped up a Rails server listening on port 3000. Go! Go right now to your browser and go to http://localhost:3000. I’ll wait.

See? Cool! It doesn’t do much yet, but we’ll change that.


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

$ ./script/generate
Usage: ./script/generate generator [options] [args]

Installed Generators
Built-in: controller, integration_test, mailer, migration, model, observer, performance_test, plugin, resource, scaffold, session_migration

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 for you — necessary for the darn thing to work, but not necessary for you to spend time writing. That’s what we have computers for, right?

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 ./script/server —help.

$ ./script/generate controller
Usage: ./script/generate controller ControllerName [options]

./script/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:
./script/generate controller ‘admin/credit_card’ suspend late_fee

Credit card admin controller with URLs /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

Ah, 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.

$ ./script/generate controller Greetings hello
exists app/controllers/
exists app/helpers/
create app/views/greetings
exists test/functional/
create app/controllers/greetings_controller.rb
create test/functional/greetings_controller_test.rb
create app/helpers/greetings_helper.rb
create app/views/greetings/hello.html.erb

Look there! Now what all did this generate? It looks like it made sure a bunch of directories were in our application, and created a controller file, a functional test file, a helper for the view, and a view file.

Let’s 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? I am exuberant!”


Then the view, to display our nice 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. Remember? ./script/server at the root of your Rails application should do it.

$ ./script/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. I’ll wait for you to be suitably impressed.

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.

“What about data, though?”, you ask over a cup of coffee. Rails comes with a generator for data models too. Can you guess its generator name?

$ ./script/generate model
Usage: ./script/generate model ModelName [field:type, field:type]

./script/generate model account

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

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.

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

$ ./script/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 public/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 public/stylesheets/scaffold.css
create app/controllers/high_scores_controller.rb
create test/functional/high_scores_controller_test.rb
create app/helpers/high_scores_helper.rb
route map.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/20081217071914_create_high_scores.rb

Taking it from the top – 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 20081217071914_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.

CAUTION: Hey. Install the sqlite3-ruby gem while you’re at it. gem install sqlite3-ruby

$ rake db:migrate
(in /home/commandsapp)
CreateHighScores: migrating
→ 0.0070s
CreateHighScores: migrated (0.0077s)

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. ./script/server; http://localhost:3000/high_scores

We can create new high scores (55,160 on Space Invaders!)


The console command lets you interact with your Rails application from the command line. On the underside, script/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.


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.


The 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.

$ ./script/plugin install


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

$ ./script/runner “Model.long_running_method”


Think of destroy as the opposite of generate. It’ll figure out what generate did, and undo it. Believe you-me, the creation of this tutorial used this command many times!

$ ./script/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
$ ./script/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


Check it: 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! about 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.

$ ./script/about
About your application’s environment
Ruby version 1.8.6 (i486-linux)
RubyGems version 1.3.1
Rails version 2.2.0
Active Record version 2.2.0
Action Pack version 2.2.0
Active Resource version 2.2.0
Action Mailer version 2.2.0
Active Support version 2.2.0
Edge Rails revision unknown
Application root /home/commandsapp
Environment development
Database adapter sqlite3
Database schema version 20081217073400

The Rails Advanced Command Line

The more advanced uses of the command line are focused around finding useful (even surprising at times) options in the utilities, and fitting utilities 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 . —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 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 script/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…
$ script/server mongrel
=> Booting Mongrel (use ‘script/server webrick’ to force WEBrick)
=> Rails 2.2.0 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 args we saved through the :assign 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:

$ ./script/generate

Installed Generators
User: tutorial_test

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

$ ./script/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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