TL;DR: from your Rails application’s root, run bin/rails generate task my_namespace my_task1 my_task2. Add code to the generated tasks, then execute one with bin/rails my_namespace:my_task1.
I’m Andrei Kaleshka, a Rails developer and the author of Rake Task Management Essentials. I originally wrote this article in 2012 after finding Rails’ task generator. Here is a complete example you can try in your own app.
Generate a Rake task
You can write a .rake file yourself, copy an existing task, or let Rails generate the skeleton:
bin/rails generate task greetings hello goodbye
The shorter form, bin/rails g task greetings hello goodbye, does the same thing. greetings is the namespace; hello and goodbye are task names. Rails creates lib/tasks/greetings.rake:
namespace :greetings do
desc "TODO"
task hello: :environment do
end
desc "TODO"
task goodbye: :environment do
end
end
Add code and run it
Replace the placeholders with descriptions and a little Ruby:
namespace :greetings do
desc "Print a greeting"
task hello: :environment do
puts "Hello from #{Rails.application.class.module_parent_name}!"
end
desc "Print a farewell"
task goodbye: :environment do
puts "Goodbye!"
end
end
Run the first task from the application root:
bin/rails greetings:hello
In an app named TaskDemo, this prints:
Hello from TaskDemo!
Run bin/rails greetings:goodbye to print Goodbye!. You can also execute these tasks with bundle exec rake greetings:hello or bundle exec rake greetings:goodbye.
What does :environment do?
task hello: :environment makes Rails’ environment task a prerequisite. It loads your application before the task body runs, so you can use application classes, models, and database queries. The greeting uses it to access Rails.application.
For a task that only uses plain Ruby, you can omit that prerequisite. For example, task :goodbye do is enough for the farewell above. Keep task bodies small: when the work grows, put the logic in an application class and call it from the task.
List your tasks
To list the tasks in this namespace:
bin/rails -T greetings
The list includes the descriptions you supplied:
bin/rails greetings:goodbye # Print a farewell
bin/rails greetings:hello # Print a greeting
-T lists tasks with a desc; an executable task without a description can be missing from this list. Use bundle exec rake -T -A greetings to include tasks without descriptions. Listing a task does not execute its body; run its full namespace:task name to do that.
See the Rails command-line guide and Rake command-line reference for more details.
Learning more
My book, Rake Task Management Essentials, covers Rake through practical examples. You can find it at Packt.
