Using Rails 3.2 (or 3.1 for that matter), you typically have CoffeeScript (and a javascript engine like therubyracer/V8) installed as gems - probably via Bundler from your Gemfile, possibly in a per-project RVM gemset.

It doesn’t seem that this type of setup includes direct access to the coffee command-line compiler. Instead the coffee-script gem uses calls directly to the compiler. Sometimes I’d just like to compile one of the CoffeeScript files in my Rails app just to look at the javascript, or maybe to export it somewhere that I’m not using CoffeeScript.

To do this, I’ve made a simple Rake task. Just drop this into lib/tasks/coffee.rake in your Rails project:

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namespace :coffee do
  task :compile, :filename do |t, args|
    filename = args.filename
    puts CoffeeScript.compile(File.open(filename))
  end
end

Then, you can compile a single file from like this:

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$ rake coffee:compile[app/assets/javascripts/mystuff.js.coffee]

This will output it to stdout so you can redirect that to a file, or the gist command, or whatever.