$ rake namespace:task['Hello,Wolrd!']

Rails task.md

# lib/tasks/task_example.rake
namespace :namespace_1 do
  # without this line the task will not be enumerated in rake -T
  desc "Description"

  task :task_name, [:params] => [:environment] do |t, arbitrary|
    # it works as splat operator
    params = arbitrary.extras.unshift arbitrary[:params] ? arbitrary[:params] : "no params"

    p params

  end

end

# run, without spaces between params: $ rake namespace_1:task_name[bla,bla2]