within implementation using Command/CompositeCommand

gistfile1.rb

require 'rspec'
require 'stringio'

class Executor
  def initialize(io)
    @io = io
  end

  def commands
    @commands ||= []
  end

  def <<(command)
    commands << command
  end

  def execute
    @commands.each { |command| io.write command.execute }
  end
end

class Command
  def initialize(command)
    @command = command
  end

  def execute
    "#{@command};"
  end
end

module DSL
  def executor
    @executor ||= Executor.new(io)
  end

  def io
    @io ||= StringIO.new
  end

  def within(target, &block)
    execute(:cd, target)
    yield
    executor.execute
  end

  def rake(task)
    execute(:rake, task)
  end

  def execute(*commands)
    executor << Command.new(commands.join(' '))
  end
end

include DSL

describe do
  before do
    within("/opt/sites/current") do
      rake "assets:precompile"
      execute :touch, 'tmp/restart.txt'
    end
  end

  it "works" do
    expect(io.string).to eq "cd /opt/sites/current;"\
      "rake assets:precompile;"\
      "touch tmp/restart.txt;"
  end
end