asset deployment with ruby on rails and rsync only if they changed

gistfile1.rb

before 'deploy:create_symlink', 'deploy:upload_assets'
before 'deploy:update_code',    'deploy:compress_assets'
after  'deploy:update_code',    'deploy:custom_symlink'

namespace :deploy do
  desc "symlinks"
  task :custom_symlink do
    run "ln -nfs #{shared_path}/assets #{release_path}/public/assets"
  end

  desc "compress assets locally"
  task :compress_assets do
    if assets_changed?
      run_locally("rm -rf public/assets/*")
      run_locally("bundle exec rake assets:precompile")
    end
  end

  desc "Upload assets"
  task :upload_assets do
    if assets_changed?
      find_servers_for_task(current_task).each do |current_server|
        run_locally("rsync --delete -avz -e ssh 'public/assets' '#{user}@#{current_server}:#{shared_path}'")
      end

      run_locally("rm -rf public/assets/*")
    end
  end

  def assets_changed?
    @changed_lines ||= begin
      deployed_sha1 = capture("cd #{current_path} && git log -1 --name-status | head -1 | awk '{print $2}'").chop
      version_to_deploy = run_locally("git ls-remote #{repository} master | awk '{print $1}'").chop
      run_locally("git log #{deployed_sha1}..#{version_to_deploy} vendor/assets/ app/assets/ | wc -l").to_i
    end
    @changed_lines > 0
  end
end