How do I pass arguments from the parent task to the child task in Rake?

Question

I am writing a Rake script which consists of tasks with arguments. I figured out how to pass arguments and how to make a task dependent on other tasks.

task :parent, [:parent_argument1, :parent_argument2, :parent_argument3] => [:child1, :child2] do
  # Perform Parent Task Functionalities
end

task :child1, [:child1_argument1, :child1_argument2] do |t, args|
  # Perform Child1 Task Functionalities
end

task :child2, [:child2_argument1, :child2_argument2] do |t, args|
  # Perform Child2 Task Functionalities
end

• Can I pass the arguments from the parent task to the child tasks?
• Is there a way to make the child tasks as private so they can't be called independently?

Answer 1

I can actually think of three ways for passing arguments between Rake tasks.

1. Use Rake’s built-in support for arguments:

   # accepts argument :one and depends on the :second task.
   task :first, [:one] => :second do |t, args|
     puts args.inspect  # => '{ :one => "one" }'
   end
   
   # argument :one was automagically passed from task :first.
   task :second, :one do |t, args|
     puts args.inspect  # => '{ :one => "one" }'
   end
   
   $ rake first[one]
   

2. Directly invoke tasks via Rake::Task#invoke:

   # accepts arguments :one, :two and passes them to the :second task.
   task :first, :one, :two do |t, args|
     puts args.inspect  # => '{ :one => "1", :two => "2" }'
     task(:second).invoke(args[:one], args[:two])
   end
   
   # accepts arguments :third, :fourth which got passed via #invoke.
   # notice that arguments are passed by position rather than name.
   task :second, :third, :fourth do |t, args|
     puts args.inspect  # => '{ :third => "1", :fourth => "2" }'
   end
   
   $ rake first[1, 2]
   

3. Another solution would be to monkey patch Rake’s main application object Rake::Application
   and use it to store arbitary values:

   class Rake::Application
     attr_accessor :my_data
   end
   
   task :first => :second do
     puts Rake.application.my_data  # => "second"
   end
   
   task :second => :third do
     puts Rake.application.my_data  # => "third"
     Rake.application.my_data = "second"
   end
   
   task :third do
     Rake.application.my_data = "third"
   end
   
   $ rake first