gistfile1.rb

before "deploy", "deploy:check_revision"

namespace :deploy do
  desc "Make sure there is something to deploy"
  task :check_revision, :roles => [:web] do
    unless `git rev-parse HEAD` == `git rev-parse origin/master`
      puts ""
      puts "  \033[1;33m**************************************************\033[0m"
      puts "  \033[1;33m* WARNING: HEAD is not the same as origin/master *\033[0m"
      puts "  \033[1;33m**************************************************\033[0m"
      puts ""

      exit
    end
  end
end