What is the best way to get an empty temporary directory in Ruby on Rails?

Question

What is the best way to get a temporary directory with nothing in it using Ruby on Rails? I need the API to be cross-platform compatible. The stdlib tmpdir won\'t work.

Answer 1

Update: gem install files, then

require "files"
dir = Files do
  file "hello.txt", "stuff"
end

See below for more examples.

---

Here's another solution, inspired by a few other answers. This one is suitable for inclusion in a test (e.g. rspec or spec_helper.rb). It makes a temporary dir based on the name of the including file, stores it in an instance variable so it persists for the duration of the test (but is not shared between tests), and deletes it on exit (or optionally doesn't, if you want to check its contents after the test run).

def temp_dir options = {:remove => true}
  @temp_dir ||= begin
    require 'tmpdir'
    require 'fileutils'
    called_from = File.basename caller.first.split(':').first, ".rb"
    path = File.join(Dir::tmpdir, "#{called_from}_#{Time.now.to_i}_#{rand(1000)}")
    Dir.mkdir(path)
    at_exit {FileUtils.rm_rf(path) if File.exists?(path)} if options[:remove]
    File.new path
  end
end

(You could also use Dir.mktmpdir (which has been around since Ruby 1.8.7) instead of Dir.mkdir but I find the API of that method confusing, not to mention the naming algorithm.)

Usage example (and another useful test method):

def write name, contents = "contents of #{name}"
  path = "#{temp_dir}/#{name}"
  File.open(path, "w") do |f|
    f.write contents
  end
  File.new path
end

describe "#write" do
  before do
    @hello = write "hello.txt"
    @goodbye = write "goodbye.txt", "farewell"
  end

  it "uses temp_dir" do
    File.dirname(@hello).should == temp_dir
    File.dirname(@goodbye).should == temp_dir
  end

  it "writes a default value" do
    File.read(@hello).should == "contents of hello.txt"
  end

  it "writes a given value" do
    # since write returns a File instance, we can call read on it
    @goodbye.read.should == "farewell" 
  end
end

---

Update: I've used this code to kickstart a gem I'm calling files which intends to make it super-easy to create directories and files for temporary (e.g. unit test) use. See https://github.com/alexch/files and https://rubygems.org/gems/files . For example:

require "files"

files = Files do     # creates a temporary directory inside Dir.tmpdir
  file "hello.txt"          # creates file "hello.txt" containing "contents of hello.txt"
  dir "web" do              # creates directory "web"
    file "snippet.html",    # creates file "web/snippet.html"...
      "
Fix this!
"  # ...containing "
Fix this!
"
    dir "img" do            # creates directory "web/img"
      file File.new("data/hello.png")            # containing a copy of hello.png
      file "hi.png", File.new("data/hello.png")  # and a copy of hello.png named hi.png
    end
  end
end                         # returns a string with the path to the directory