cap deployment detection code

is_cap.rb

# this method method will return true if it appears your rail's app is running
# in a cap deployment.  given a block, it will run that block only if the app
# has been deployed via cap
#
  def cap?(&block)
    realpath = proc do |path|
      begin
        (path.is_a?(Pathname) ? path : Pathname.new(path.to_s)).realpath.to_s
      rescue Errno::ENOENT
        nil
      end
    end

    rails_root = realpath[Rails.root]

    shared_path = File.expand_path('../../shared', rails_root)
    cap_path = File.dirname(shared_path)
    shared_public_system_path = File.expand_path('../../shared/system')

    public_path = Rails.public_path.to_s
    public_system_path = File.join(Rails.public_path.to_s, 'system')
 
    is_cap_deploy =
      test(?e, shared_public_system_path) and
      test(?l, public_system_path) and
      realpath[shared_public_system_path] == realpath[public_system_path]

    return false unless is_cap_deploy

    block ? block.call(*[cap_path].slice(0, block.arity)) : cap_path
  end