require "dry/cli"

module Foo
  module Commands
    extend Dry::CLI::Registry

    module Generate
      class App < Dry::CLI::Command
      end

      class Action < Dry::CLI::Command
      end
    end

    register "generate", aliases: ["g"] do |prefix|
      prefix.register "app",    Generate::App
      prefix.register "action", Generate::Action
    end
  end
end

Description:

here you can include a general documentation about the subcommand.

Commands:
  foo.rb generate action
  foo.rb generate app

    register "generate", aliases: ["g"] do |prefix|
      prefix.desc 'HERE YOU CAN INCLUDE THE DOCUMENTATION OF THE COMMAND'
      prefix.register "app",    Generate::App
      prefix.register "action", Generate::Action
    end