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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.

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:

rails console
rails server
bin/rails
rails generate
rails dbconsole
rails new app_name

All commands can run with -h or --help to list more information.

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.

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

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

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.

`rails server`

The 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, rails server will run our new shiny Rails app:

$ cd commandsapp
$ bin/rails server
=> Booting Puma
=> Rails 5.1.0 application starting in development on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options
Puma starting in single mode...
* Version 3.0.2 (ruby 2.3.0-p0), codename: Plethora of Penguin Pinatas
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://localhost: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.

INFO: You can also use the alias "s" to start the server: 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.

`rails generate`

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

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

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

...
...

Please choose a generator below.

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

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.

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.

$ bin/rails generate controller
Usage: 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:
    `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  assets
     invoke    coffee
     create      app/assets/javascripts/greetings.coffee
     invoke    scss
     create      app/assets/stylesheets/greetings.scss

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?"
  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 rails server.

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

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.

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

...

Active Record options:
      [--migration]            # Indicates when to generate migration
                               # Default: true

...

Description:
    Create rails files for model generator.

NOTE: 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/20130717151933_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
    invoke    helper
    create      app/helpers/high_scores_helper.rb
    invoke    jbuilder
    create      app/views/high_scores/index.json.jbuilder
    create      app/views/high_scores/show.json.jbuilder
    invoke  test_unit
    create    test/system/high_scores_test.rb
    invoke  assets
    invoke    coffee
    create      app/assets/javascripts/high_scores.coffee
    invoke    scss
    create      app/assets/stylesheets/high_scores.scss
    invoke  scss
   identical    app/assets/stylesheets/scaffolds.scss

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 20130717151933_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 bin/rails db:migrate command. We'll talk more about bin/rails in-depth in a little while.

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

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. 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!)

`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.

INFO: You can also use the alias "c" to invoke the console: 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 rails console --sandbox.

$ bin/rails console --sandbox
Loading development environment in sandbox (Rails 5.1.0)
Any modifications you make will be rolled back on exit
irb(main):001:0>

The app and helper objects

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

With the app method you can access url and path helpers, as well as do requests.

>> app.root_path
=> "/"

>> 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.

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

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

`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 (including MariaDB), PostgreSQL and SQLite3.

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

`rails runner`

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

$ bin/rails runner "Model.long_running_method"

INFO: You can also use the alias "r" to invoke the runner: 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

`rails destroy`

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

INFO: You can also use the alias "d" to invoke the destroy command: 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

bin/rails

Since Rails 5.0+ has rake commands built into the rails executable, bin/rails is the new default for running commands.

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

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

The most common rails 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                    Loads fixtures into the ...
db:migrate                          Migrate the database ...
db:migrate:status                   Display status of migrations
db:rollback                         Rolls the schema back to ...
db:schema:cache:clear               Clears a db/schema_cache.yml file
db:schema:cache:dump                Creates a db/schema_cache.yml file
db:schema:dump                      Creates a db/schema.rb file ...
db:schema:load                      Loads a schema.rb file ...
db:seed                             Loads the seed data ...
db:structure:dump                   Dumps the database structure ...
db:structure:load                   Recreates the databases ...
db:version                          Retrieves the current schema ...
...
restart                             Restart app by touching ...
tmp:create                          Creates tmp directories ...

INFO: You can also use bin/rails -T to get the list of tasks.

`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             5.1.0
Ruby version              2.2.2 (x86_64-linux)
RubyGems version          2.4.6
Rack version              2.0.1
JavaScript Runtime        Node.js (V8)
Middleware:               Rack::Sendfile, ActionDispatch::Static, ActionDispatch::Executor, 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::Reloader, ActionDispatch::Callbacks, ActiveRecord::Migration::CheckPending, ActionDispatch::Cookies, ActionDispatch::Session::CookieStore, ActionDispatch::Flash, Rack::Head, Rack::ConditionalGet, Rack::ETag
Application root          /home/foobar/commandsapp
Environment               development
Database adapter          sqlite3
Database schema version   20110805173523

`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 task 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.

`db`

The most common tasks of the db: bin/rails namespace are migrate and create, and it will pay off to try out all of the migration bin/rails tasks (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.

`notes`

bin/rails notes will search through your code for comments beginning with FIXME, OPTIMIZE or TODO. The search is done in files with extension .builder, .rb, .rake, .yml, .yaml, .ruby, .css, .js and .erb for both default and custom annotations.

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

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

You can add support for new file extensions using config.annotations.register_extensions option, which receives a list of the extensions with its corresponding regex to match it up.

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

If you are looking for a specific annotation, say FIXME, you can use bin/rails notes:fixme. Note that you have to lower case the annotation's name.

$ bin/rails notes:fixme
(in /home/foobar/commandsapp)
app/controllers/admin/users_controller.rb:
  * [132] high priority for next deploy

app/models/school.rb:
  * [ 17]

You can also use custom annotations in your code and list them using bin/rails notes:custom by specifying the annotation using an environment variable ANNOTATION.

$ bin/rails notes:custom ANNOTATION=BUG
(in /home/foobar/commandsapp)
app/models/article.rb:
  * [ 23] Have to fix this one before pushing!

NOTE. When using specific annotations and custom annotations, the annotation name (FIXME, BUG etc) is not displayed in the output lines.

By default, rails notes will look in the app, config, db, lib and test directories. If you would like to search other directories, you can configure them using config.annotations.register_directories option.

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

You can also provide them as a comma separated list in the environment variable SOURCE_ANNOTATION_DIRECTORIES.

$ export SOURCE_ANNOTATION_DIRECTORIES='spec,vendor'
$ bin/rails notes
(in /home/foobar/commandsapp)
app/models/user.rb:
  * [ 35] [FIXME] User should have a subscription at this point
spec/models/user_spec.rb:
  * [122] [TODO] Verify the user that has a subscription works

`routes`

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.

`test`

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 Minitest. Rails owes its stability to the use of tests. The tasks available in the test: namespace helps in running the different tests you will hopefully write.

`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 tasks will help you clear and create the Rails.root/tmp directory:

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

Miscellaneous

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.
rails secret will give you a pseudo-random key to use for your session secret.
rails time:zones:all lists all the timezones Rails knows about.

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 db:nothing

NOTE: If your 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.

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
      exists
      create  app/controllers
      create  app/helpers
...
...
      create  tmp/cache
      create  tmp/pids
      create  Rakefile
add 'Rakefile'
      create  README.md
add 'README.md'
      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
# PostgreSQL. Versions 9.1 and up are supported.
#
# Install the pg driver:
#   gem install pg
# On OS X with Homebrew:
#   gem install pg -- --with-pg-config=/usr/local/bin/pg_config
# On OS X with MacPorts:
#   gem install pg -- --with-pg-config=/opt/local/lib/postgresql84/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
  # http://guides.rubyonrails.org/configuring.html#database-pooling
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>

development:
  <<: *default
  database: gitapp_development
...
...

It also generated some lines in our database.yml configuration corresponding to our choice of PostgreSQL for database.

NOTE. 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.