Ruby的Rake工具其实是模仿的Make，我们写一个简单的Rakefile看看:

desc "Rake Test"
task :main
  puts "Hello, Rake!"
  
task :default => :main

然后我们在Rakefile当前目录运行rake或rake -f Rakefile即可
其中我们定义了一个main task，并且将其设为默认task
我们再看看怎样写结合Rails的Rakefile,Rails在lib/tasks目录里查找并加载所有以.rake作为后缀名的Rakefile，如lib/tasks/load_musicians.rake:

desc "Load musicians and the instruments they play into the database."
task :load_musicians => ['musicians.csv', :environment] do |t|
  before_count = Musicians.count
  File.read(t.prerequisites.first).each do |line|
    given_name, surname, instrument = line.split(/,/)
    Musician.create(:given_name => given_name,
                    :surname => surname,
                    :instrument => instrument)
  end
  puts "Loaded #{Musicians.count - before_count} musicians."
end

然后我们可以运行rake load_musicians命令来调用load_musicians task
该task的dependency列表中包含:environment，这是用来初始化Rails环境以及建立数据库连接
如果我们自定义的task需要migrate，则我们可以这样写:

task :load_musicians => ['musicians.csv', :migrate] do |t|

则我们运行该task时会先rake db:migrate，而且:migrate已经初始化了Rails环境，我们不用再写:environment了