Thor executable and tasks in separate file(s).

common.thor

# coding: utf-8

class Top < Thor
  include Thor::Actions

  class << self
    def baz
      puts 'baz'
    end
  end

  module Util
    def myputs(arg)
      say arg, :red
    end
  end
end

exe

#!/usr/bin/env ruby
# coding: utf-8

require 'thor'
require 'thor/runner'

Thor::Util.load_thorfile('./common.thor')

$thor_runner = true
Thor::Runner.start

# give this file +x permission:
# chmod +x exe

othertasks.thor

# coding: utf-8

class Top < Thor
  desc "bar", "top:bar's description"
  def bar
    p self.class
    Top::baz
  end

  class Foo < Thor
    include Top::Util
    namespace :foo

    desc "bar", "foo:bar's description"
    def bar(arg)
      p self.class
      Top::baz
      myputs(arg)
    end
  end
end