Rake task to automatically run something (i.e. specs) when code files are changed

on_update.task.rb

# Rake task to automatically run something (i.e. specs) when code files are changed
# By Peter Çoopér
#
# Motivation: I couldn't get autotest to run on my Sinatra project for some reason but realized
# it didn't require overengineering. Just detect when a file is changed and then re-run the specs!
#
# Examples:
#      # rake on_update "rake"
#      # rake on_update "spec spec/user_spec.rb"
#
# Installation: Just add this Rake task into your Rakefile or whatever task inclusion system
# you have set up.
#
# License: Public domain.

desc "Automatically run something when code is changed"
task :on_update do
  require 'find'
  files = {}

  loop do
    changed = false
    Find.find(File.dirname(__FILE__)) do |file|
      next unless file =~ /\.rb$/
      ctime = File.ctime(file).to_i

      if ctime != files[file]
        files[file] = ctime
        changed = true
      end
    end

    if changed
      system ARGV[1]
      puts "\nWaiting for a *.rb change"
    end

    sleep 1
  end
end

Have you looking into watchr? One benefit I see with watchr is that it's platform agnostic...incase you want to use it in other platforms/systems