How Rake runs its top level.

mycmd.rb

# Sample custom rake-like command supporting three options.
#
#   mycmd start
#   mycmd stop
#   mycmd restart

require 'rake'

Rake.application.init('mycmd')

task :start do ... end
task :stop  do ... end
task :restart do ... end

Rake.application.top_level

rake_application_snippet.rb

# Snippet of code from Rake/application.rb ...

    # Run the Rake application.  The run method performs the following
    # three steps:
    #
    # * Initialize the command line options (+init+).
    # * Define the tasks (+load_rakefile+).
    # * Run the top level tasks (+top_level+).
    #
    # If you wish to build a custom rake command, you should call
    # +init+ on your application.  Then define any tasks.  Finally,
    # call +top_level+ to run your top level tasks.
    #
    def run
      standard_exception_handling do
        init
        load_rakefile
        top_level
      end
    end