gistfile1.sh

22:55:19 guillermo@leuschnerdamm:/tmp/asdf  ruby-1.9.2-p290 
$ rake install
Installing
Installing
22:56:07 guillermo@leuschnerdamm:/tmp/asdf  ruby-1.9.2-p290 
$ rake install2
WADUS WADUS
22:56:09 guillermo@leuschnerdamm:/tmp/asdf  ruby-1.9.2-p290 
$ 


The second method is only possible with newer version of rake. Old ones use top level binding to execute code.

my_lib.rb

# Require always use TOPLEVEL_BINDING
# so next method will be there
 
def install
  puts "WADUS WADUS"
end

Rakefile

# Option 1
# The clean one, you can move the class to other file
module Utils
  extend self

  def install
    puts "Installing"
  end
end

desc "We are going to install... LA LA LA"
task :install do
  Utils::install
  Utils.install # You can use whatever you want
end


# Option 2
# You can use a separete file. 
$:.unshift(File.dirname(__FILE__)) # current dir is not included

require 'my_file'

desc "We are going to install... LA LA LA"
task :install2 do
  TOPLEVEL_BINDING.instance_exec{ install }
end