Some overlooked features of Rake, Ruby's build tool

Rakefile

require 'yaml'
require 'json'
require 'logger'

# Some useful, and often overlooked features of Rake, Ruby's build tool.

directory "logs"
desc "Log tasks execution to a file"
task "log" => ['logs'] do
  MyLogger.instance
end

directory "foo/bar/baz"
desc "Write stuff"
file "foo/bar/baz/stuff.txt" => ['log', 'foo/bar/baz'] do
  MyLogger.instance.info "writing stuff.txt"

  File.open("foo/bar/baz/stuff.txt", "w") do |f|
    f.write("bla bla bla")
  end

  MyLogger.instance.info "done writing stuff.txt"
end

desc "write more stuff"
file "foo/bar/baz/more_stuff.txt" => ['foo/bar/baz/stuff.txt'] do
  File.open("foo/bar/baz/more_stuff.txt", "w") do |f|
    f.write("more stuff")
  end

  MyLogger.instance.info "written even more_stuff.txt"
end

desc "Automagically synthesise a task for converting JSON files into YAML."
directory "yamls"
rule /\.yml$/ => [
    proc { |task_name| "json/#{File.basename(task_name, '.yml')}.json" },
    'yamls',
    'log'
  ] do |t|

  data = JSON.parse(File.read(t.source))
  MyLogger.instance.info "writing document #{t.name}"

  File.open(t.name, "w+") do |f|
    f.write(data.to_yaml)
  end
end

class MyLogger < Logger
  def self.instance
    @logger ||= Logger.new("logs/#{build_id}.log")
  end
  def self.build_id
    @build_id ||= Time.now.to_i
  end
end