Capistrano: prompt to confirm branch if not on master

gistfile1.rb

def current_git_branch
  `git symbolic-ref HEAD`.gsub("refs/heads/", "")
end

def prompt_with_default(message, default)
  response = Capistrano::CLI.ui.ask "#{message} Default is: [#{default}] : "
  response.empty? ? default : response
end

def set_branch
  if current_git_branch != "master"
    set :branch, ENV['BRANCH'] || prompt_with_default("Enter branch to deploy, or ENTER for default.", "master")
  else
    set :branch, ENV['BRANCH'] || "master"
  end
end