The Rails Command Line

After reading this guide, you will know:

How to create a Rails application.
How to generate models, controllers, database migrations, and unit tests.
How to start a development server.
How to experiment with objects through an interactive shell.

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

1 Creating a Rails App

First, let's create a simple Rails application using the rails new command.

We will use this application to play and discover all the commands described in this guide.

You can install the rails gem by typing gem install rails, if you don't have it already.

1.1 `rails new`

The first argument we'll pass to the rails new command is the application name.

$ rails new my_app
     create
     create  README.md
     create  Rakefile
     create  config.ru
     create  .gitignore
     create  Gemfile
     create  app
     ...
     create  tmp/cache
     ...
        run  bundle install

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

If you wish to skip some files from being generated or skip some libraries, you can append any of the following arguments to your rails new command:

Argument	Description
`--skip-git`	Skip git init, .gitignore, and .gitattributes
`--skip-docker`	Skip Dockerfile, .dockerignore and bin/docker-entrypoint
`--skip-keeps`	Skip source control .keep files
`--skip-action-mailer`	Skip Action Mailer files
`--skip-action-mailbox`	Skip Action Mailbox gem
`--skip-action-text`	Skip Action Text gem
`--skip-active-record`	Skip Active Record files
`--skip-active-job`	Skip Active Job
`--skip-active-storage`	Skip Active Storage files
`--skip-action-cable`	Skip Action Cable files
`--skip-asset-pipeline`	Skip Asset Pipeline
`--skip-javascript`	Skip JavaScript files
`--skip-hotwire`	Skip Hotwire integration
`--skip-jbuilder`	Skip jbuilder gem
`--skip-test`	Skip test files
`--skip-system-test`	Skip system test files
`--skip-bootsnap`	Skip bootsnap gem
`--skip-dev-gems`	Skip adding development gems
`--skip-thruster`	Skip Thruster setup
`--skip-rubocop`	Skip RuboCop setup
`--skip-brakeman`	Skip brakeman setup
`--skip-ci`	Skip GitHub CI files
`--skip-kamal`	Skip Kamal setup
`--skip-solid`	Skip Solid Cache, Queue, and Cable setup

These are just some of the options that rails new accepts. For a full list of options, type rails new --help.

1.2 Preconfigure a Different Database

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

Let's see what a --database=postgresql option will do for us:

$ rails new petstore --database=postgresql
      create
      create  app/controllers
      create  app/helpers
...

Let's see what it put in our config/database.yml:

# PostgreSQL. Versions 9.3 and up are supported.
#
# Install the pg driver:
#   gem install pg
# On macOS with Homebrew:
#   gem install pg -- --with-pg-config=/usr/local/bin/pg_config
# On Windows:
#   gem install pg
#       Choose the win32 build.
#       Install PostgreSQL and put its /bin directory on your path.
#
# Configure Using Gemfile
# gem "pg"
#
default: &default
  adapter: postgresql
  encoding: unicode

  # For details on connection pooling, see Rails configuration guide
  # https://guides.rubyonrails.org/configuring.html#database-pooling
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>

development:
  <<: *default
  database: petstore_development
...

It generated a database configuration corresponding to our choice of PostgreSQL.

2 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:

bin/rails console
bin/rails server
bin/rails test
bin/rails generate
bin/rails db:migrate
bin/rails db:create
bin/rails routes
bin/rails dbconsole
rails new app_name

You can get a list of rails commands available to you, which will often depend on your current directory, by typing rails --help. Each command has a description, and should help you find the thing you need.

$ rails --help
Usage:
  bin/rails COMMAND [options]

You must specify a command. The most common commands are:

  generate     Generate new code (short-cut alias: "g")
  console      Start the Rails console (short-cut alias: "c")
  server       Start the Rails server (short-cut alias: "s")
  ...

All commands can be run with -h (or --help) for more information.

In addition to those commands, there are:
about                               List versions of all Rails ...
assets:clean[keep]                  Remove old compiled assets
assets:clobber                      Remove compiled assets
assets:environment                  Load asset compile environment
assets:precompile                   Compile all the assets ...
...
db:fixtures:load                    Load fixtures into the ...
db:migrate                          Migrate the database ...
db:migrate:status                   Display status of migrations
db:rollback                         Roll the schema back to ...
db:schema:cache:clear               Clears a db/schema_cache.yml file
db:schema:cache:dump                Create a db/schema_cache.yml file
db:schema:dump                      Create a database schema file (either db/schema.rb or db/structure.sql ...
db:schema:load                      Load a database schema file (either db/schema.rb or db/structure.sql ...
db:seed                             Load the seed data ...
db:version                          Retrieve the current schema ...
...
restart                             Restart app by touching ...
tmp:create                          Create tmp directories ...

2.1 `bin/rails server`

The bin/rails server command launches a web server named Puma which comes bundled with Rails. You'll use this any time you want to access your application through a web browser.

With no further work, bin/rails server will run our new shiny Rails app:

$ cd my_app
$ bin/rails server
=> Booting Puma
=> Rails 8.0.0 application starting in development
=> Run `bin/rails server --help` for more startup options
Puma starting in single mode...
* Puma version: 6.4.0 (ruby 3.1.3-p185) ("The Eagle of Durango")
*  Min threads: 5
*  Max threads: 5
*  Environment: development
*          PID: 5295
* Listening on http://127.0.0.1:3000
* Listening on http://[::1]:3000
Use Ctrl-C to stop

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: bin/rails s.

The server can be run on a different port using the -p option. The default development environment can be changed using -e.

$ bin/rails server -e production -p 4000

The -b option binds Rails to the specified IP, by default it is localhost. You can run a server as a daemon by passing a -d option.

2.2 `bin/rails generate`

The bin/rails generate command uses templates to create a whole lot of things. Running bin/rails generate by itself gives a list of available generators:

You can also use the alias "g" to invoke the generator command: bin/rails g.

$ bin/rails generate
Usage:
  bin/rails generate GENERATOR [args] [options]

...
...

Please choose a generator below.

Rails:
  assets
  channel
  controller
  generator
  ...
  ...

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.

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

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

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

...
...

Description:
    ...

    To create a controller within a module, specify the controller name as a path like 'parent_module/controller_name'.

    ...

Example:
    `bin/rails generate controller CreditCards open debit credit close`

    Credit card controller with URLs like /credit_cards/debit.
        Controller: app/controllers/credit_cards_controller.rb
        Test:       test/controllers/credit_cards_controller_test.rb
        Views:      app/views/credit_cards/debit.html.erb [...]
        Helper:     app/helpers/credit_cards_helper.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.

$ bin/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/controllers/greetings_controller_test.rb
     invoke  helper
     create    app/helpers/greetings_helper.rb
     invoke    test_unit

What did all 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?"
  end
end

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

<h1>A Greeting for You!</h1>
<p><%= @message %></p>

Fire up your server using bin/rails server.

$ bin/rails server
=> Booting Puma...

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

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.

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

...

ActiveRecord options:
      [--migration], [--no-migration]        # Indicates when to generate migration
                                             # Default: true

...

Description:
    Generates a new model. Pass the model name, either CamelCased or
    under_scored, and an optional list of attribute pairs as arguments.

...

For a list of available field types for the type parameter, refer to the API documentation for the add_column method for the SchemaStatements module. The index parameter generates a corresponding index for the column.

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.

$ bin/rails generate scaffold HighScore game:string score:integer
    invoke  active_record
    create    db/migrate/20190416145729_create_high_scores.rb
    create    app/models/high_score.rb
    invoke    test_unit
    create      test/models/high_score_test.rb
    create      test/fixtures/high_scores.yml
    invoke  resource_route
     route    resources :high_scores
    invoke  scaffold_controller
    create    app/controllers/high_scores_controller.rb
    invoke    erb
    create      app/views/high_scores
    create      app/views/high_scores/index.html.erb
    create      app/views/high_scores/edit.html.erb
    create      app/views/high_scores/show.html.erb
    create      app/views/high_scores/new.html.erb
    create      app/views/high_scores/_form.html.erb
    invoke    test_unit
    create      test/controllers/high_scores_controller_test.rb
    create      test/system/high_scores_test.rb
    invoke    helper
    create      app/helpers/high_scores_helper.rb
    invoke      test_unit
    invoke    jbuilder
    create      app/views/high_scores/index.json.jbuilder
    create      app/views/high_scores/show.json.jbuilder
    create      app/views/high_scores/_high_score.json.jbuilder

The generator creates the model, views, controller, resource route, and database migration (which creates the high_scores table) for HighScore. And it adds tests for those.

The migration requires that we migrate, that is, run some Ruby code (the 20190416145729_create_high_scores.rb file from the above output) to modify the schema of our database. Which database? The SQLite3 database that Rails will create for you when we run the bin/rails db:migrate command. We'll talk more about that command below.

$ bin/rails db:migrate
==  CreateHighScores: migrating ===============================================
-- create_table(:high_scores)
   -> 0.0017s
==  CreateHighScores: migrated (0.0019s) ======================================

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. Please visit the testing guide for an in-depth look at unit testing.

Let's see the interface Rails created for us.

$ bin/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!)

2.3 `bin/rails console`

The console command lets you interact with your Rails application from the command line. On the underside, bin/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: bin/rails c.

You can specify the environment in which the console command should operate.

$ bin/rails console -e staging

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

$ bin/rails console --sandbox
Loading development environment in sandbox (Rails 8.0.0)
Any modifications you make will be rolled back on exit
irb(main):001:0>

2.3.1 The `app` and `helper` Objects

Inside the bin/rails console you have access to the app and helper instances.

With the app method you can access named route helpers, as well as do requests.

irb> app.root_path
=> "/"

irb> app.get _
Started GET "/" for 127.0.0.1 at 2014-06-19 10:41:57 -0300
...

With the helper method it is possible to access Rails and your application's helpers.

irb> helper.time_ago_in_words 30.days.ago
=> "about 1 month"

irb> helper.my_custom_helper
=> "my custom helper"

2.4 `bin/rails dbconsole`

bin/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 (including MariaDB), PostgreSQL, and SQLite3.

You can also use the alias "db" to invoke the dbconsole: bin/rails db.

If you are using multiple databases, bin/rails dbconsole will connect to the primary database by default. You can specify which database to connect to using --database or --db:

$ bin/rails dbconsole --database=animals

2.5 `bin/rails runner`

runner runs Ruby code in the context of the Rails application non-interactively, without having to open Rails console. For instance:

$ bin/rails runner "Model.long_running_method"

You can also use the alias "r" to invoke the runner: bin/rails r.

You can specify the environment in which the runner command should operate using the -e switch.

$ bin/rails runner -e staging "Model.long_running_method"

You can even execute ruby code written in a file with runner.

$ bin/rails runner lib/code_to_be_run.rb

By default, rails runner scripts are automatically wrapped with the Rails Executor, which helps report uncaught exceptions for tasks like cron jobs.

Therefore, executing rails runner lib/long_running_scripts.rb is functionally equivalent to the following:

Rails.application.executor.wrap do
  # executes code inside lib/long_running_scripts.rb
end

You can opt out of this behaviour by using the --skip-executor option.

$ bin/rails runner --skip-executor lib/long_running_script.rb

2.6 `bin/rails destroy`

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

You can also use the alias "d" to invoke the destroy command: bin/rails d.

$ bin/rails generate model Oops
      invoke  active_record
      create    db/migrate/20120528062523_create_oops.rb
      create    app/models/oops.rb
      invoke    test_unit
      create      test/models/oops_test.rb
      create      test/fixtures/oops.yml

$ bin/rails destroy model Oops
      invoke  active_record
      remove    db/migrate/20120528062523_create_oops.rb
      remove    app/models/oops.rb
      invoke    test_unit
      remove      test/models/oops_test.rb
      remove      test/fixtures/oops.yml

2.7 `bin/rails about`

bin/rails 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.

$ bin/rails about
About your application's environment
Rails version             8.0.0
Ruby version              3.2.0 (x86_64-linux)
RubyGems version          3.3.7
Rack version              3.0.8
JavaScript Runtime        Node.js (V8)
Middleware:               ActionDispatch::HostAuthorization, Rack::Sendfile, ActionDispatch::Static, ActionDispatch::Executor, ActionDispatch::ServerTiming, ActiveSupport::Cache::Strategy::LocalCache::Middleware, Rack::Runtime, Rack::MethodOverride, ActionDispatch::RequestId, ActionDispatch::RemoteIp, Sprockets::Rails::QuietAssets, Rails::Rack::Logger, ActionDispatch::ShowExceptions, WebConsole::Middleware, ActionDispatch::DebugExceptions, ActionDispatch::ActionableExceptions, ActionDispatch::Reloader, ActionDispatch::Callbacks, ActiveRecord::Migration::CheckPending, ActionDispatch::Cookies, ActionDispatch::Session::CookieStore, ActionDispatch::Flash, ActionDispatch::ContentSecurityPolicy::Middleware, ActionDispatch::PermissionsPolicy::Middleware, Rack::Head, Rack::ConditionalGet, Rack::ETag, Rack::TempfileReaper
Application root          /home/foobar/my_app
Environment               development
Database adapter          sqlite3
Database schema version   20180205173523

2.8 `bin/rails assets:`

You can precompile the assets in app/assets using bin/rails assets:precompile, and remove older compiled assets using bin/rails assets:clean. The assets:clean command allows for rolling deploys that may still be linking to an old asset while the new assets are being built.

If you want to clear public/assets completely, you can use bin/rails assets:clobber.

2.9 `bin/rails db:`

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

More information about migrations can be found in the Migrations guide.

2.10 `bin/rails notes`

bin/rails notes searches through your code for comments beginning with a specific keyword. You can refer to bin/rails notes --help for information about usage.

By default, it will search in app, config, db, lib, and test directories for FIXME, OPTIMIZE, and TODO annotations in files with extension .builder, .rb, .rake, .yml, .yaml, .ruby, .css, .js, and .erb.

$ bin/rails notes
app/controllers/admin/users_controller.rb:
  * [ 20] [TODO] any other way to do this?
  * [132] [FIXME] high priority for next deploy

lib/school.rb:
  * [ 13] [OPTIMIZE] refactor this code to make it faster
  * [ 17] [FIXME]

2.10.1 Annotations

You can pass specific annotations by using the --annotations argument. By default, it will search for FIXME, OPTIMIZE, and TODO. Note that annotations are case sensitive.

$ bin/rails notes --annotations FIXME RELEASE
app/controllers/admin/users_controller.rb:
  * [101] [RELEASE] We need to look at this before next release
  * [132] [FIXME] high priority for next deploy

lib/school.rb:
  * [ 17] [FIXME]

2.10.2 Tags

You can add more default tags to search for by using config.annotations.register_tags. It receives a list of tags.

config.annotations.register_tags("DEPRECATEME", "TESTME")

$ bin/rails notes
app/controllers/admin/users_controller.rb:
  * [ 20] [TODO] do A/B testing on this
  * [ 42] [TESTME] this needs more functional tests
  * [132] [DEPRECATEME] ensure this method is deprecated in next release

2.10.3 Directories

You can add more default directories to search from by using config.annotations.register_directories. It receives a list of directory names.

config.annotations.register_directories("spec", "vendor")

$ bin/rails notes
app/controllers/admin/users_controller.rb:
  * [ 20] [TODO] any other way to do this?
  * [132] [FIXME] high priority for next deploy

lib/school.rb:
  * [ 13] [OPTIMIZE] Refactor this code to make it faster
  * [ 17] [FIXME]

spec/models/user_spec.rb:
  * [122] [TODO] Verify the user that has a subscription works

vendor/tools.rb:
  * [ 56] [TODO] Get rid of this dependency

2.10.4 Extensions

You can add more default file extensions to search from by using config.annotations.register_extensions. It receives a list of extensions with its corresponding regex to match it up.

config.annotations.register_extensions("scss", "sass") { |annotation| /\/\/\s*(#{annotation}):?\s*(.*)$/ }

$ bin/rails notes
app/controllers/admin/users_controller.rb:
  * [ 20] [TODO] any other way to do this?
  * [132] [FIXME] high priority for next deploy

app/assets/stylesheets/application.css.sass:
  * [ 34] [TODO] Use pseudo element for this class

app/assets/stylesheets/application.css.scss:
  * [  1] [TODO] Split into multiple components

lib/school.rb:
  * [ 13] [OPTIMIZE] Refactor this code to make it faster
  * [ 17] [FIXME]

spec/models/user_spec.rb:
  * [122] [TODO] Verify the user that has a subscription works

vendor/tools.rb:
  * [ 56] [TODO] Get rid of this dependency

2.11 `bin/rails routes`

bin/rails 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.

2.12 `bin/rails test`

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

Rails comes with a test framework called minitest. Rails owes its stability to the use of tests. The commands available in the test: namespace helps in running the different tests you will hopefully write.

2.13 `bin/rails tmp:`

The Rails.root/tmp directory is, like the *nix /tmp directory, the holding place for temporary files like process id files and cached actions.

The tmp: namespaced commands will help you clear and create the Rails.root/tmp directory:

bin/rails tmp:cache:clear clears tmp/cache.
bin/rails tmp:sockets:clear clears tmp/sockets.
bin/rails tmp:screenshots:clear clears tmp/screenshots.
bin/rails tmp:clear clears all cache, sockets, and screenshot files.
bin/rails tmp:create creates tmp directories for cache, sockets, and pids.

2.14 Miscellaneous

bin/rails initializers prints out all defined initializers in the order they are invoked by Rails.
bin/rails middleware lists Rack middleware stack enabled for your app.
bin/rails 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.
bin/rails secret will give you a pseudo-random key to use for your session secret.
bin/rails time:zones:all lists all the timezones Rails knows about.
bin/rails boot boots the application and exits.

2.15 Custom Rake Tasks

Custom rake tasks have a .rake extension and are placed in Rails.root/lib/tasks. You can create these custom rake tasks with the bin/rails generate task command.

desc "I am short, but comprehensive description for my cool task"
task task_name: [:prerequisite_task, :another_task_we_depend_on] do
  # All your magic here
  # Any valid Ruby code is allowed
end

To pass arguments to your custom rake task:

task :task_name, [:arg_1] => [:prerequisite_1, :prerequisite_2] do |task, args|
  argument_1 = args.arg_1
end

You can group tasks by placing them in namespaces:

namespace :db do
  desc "This task does nothing"
  task :nothing do
    # Seriously, nothing
  end
end

Invocation of the tasks will look like:

$ bin/rails task_name
$ bin/rails "task_name[value 1]" # entire argument string should be quoted
$ bin/rails "task_name[value 1,value2,value3]" # separate multiple args with a comma
$ bin/rails db:nothing

If you need to interact with your application models, perform database queries, and so on, your task should depend on the environment task, which will load your application code.

task task_that_requires_app_code: [:environment] do
  User.create!
end