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Ruby Koans

The Ruby Koans walk you along the path to enlightenment in order to learn Ruby. The goal is to learn the Ruby language, syntax, structure, and some common functions and libraries. We also teach you culture by basing the koans on tests. Testing is not just something we pay lip service to, but something we live. Testing is essential in your quest to learn and do great things in Ruby.

The Structure

The koans are broken out into areas by file, hashes are covered in about_hashes.rb, modules are introduced in about_modules.rb, etc. They are presented in order in the path_to_enlightenment.rb file.

Each koan builds up your knowledge of Ruby and builds upon itself. It will stop at the first place you need to correct.

Some koans simply need to have the correct answer substituted for an incorrect one. Some, however, require you to supply your own answer. If you see the method __ (a double underscore) listed, it is a hint to you to supply your own code in order to make it work correctly.

Installing Ruby

If you do not have Ruby setup, please visit for operating specific instructions. In order to run the koans you need ruby and rake installed. To check your installations simply type:

*nix platforms from any terminal window:

[~] $ ruby --version
[~] $ rake --version

Windows from the command prompt (cmd.exe)

c:\ruby --version
c:\rake --version

If you don't have rake installed, just run gem install rake

Any response for Ruby with a version number greater than 1.8 is fine (should be around 1.8.6 or more). Any version of rake will do.

Generating the Koans

A fresh checkout will not include the koans, you will need to generate them.

[ruby_koans] $ rake gen                       # generates the koans directory

If you need to regenerate the koans, thus wiping your current `koans`,

[ruby_koans] $ rake regen                     # regenerates the koans directory, wiping the original

The Path To Enlightenment

You can run the tests through rake or by calling the file itself (rake is the recommended way to run them as we might build more functionality into this task).

*nix platforms, from the ruby_koans directory

[ruby_koans] $ rake                           # runs the default target :walk_the_path
[ruby_koans] $ ruby path_to_enlightenment.rb  # simply call the file directly

Windows is the same thing

c:\ruby_koans\rake                             # runs the default target :walk_the_path
c:\ruby_koans\ruby path_to_enlightenment.rb    # simply call the file directly

Red, Green, Refactor

In test-driven development the mantra has always been red, green, refactor. Write a failing test and run it (red), make the test pass (green), then look at the code and consider if you can make it any better (refactor).

While walking the path to Ruby enlightenment you will need to run the koan and see it fail (red), make the test pass (green), then take a moment and reflect upon the test to see what it is teaching you and improve the code to better communicate its intent (refactor).

The very first time you run the koans you will see the following output:

[ ruby_koans ] $ rake
(in /Users/person/dev/ruby_koans)
/usr/bin/ruby1.8 path_to_enlightenment.rb

AboutAsserts#test_assert_truth has damaged your karma.

The Master says:
You have not yet reached enlightenment.

The answers you seek...
<false> is not true.

Please meditate on the following code:
./about_asserts.rb:10:in `test_assert_truth'
path_to_enlightenment.rb:38:in `each_with_index'

mountains are merely mountains
your path thus far [X_________________________________________________] 0/280 (0%)

You have come to your first stage. Notice it is telling you where to look for the first solution:

Please meditate on the following code:
./about_asserts.rb:10:in `test_assert_truth'
path_to_enlightenment.rb:38:in `each_with_index'

Open the about_asserts.rb file and look at the first test:

# We shall contemplate truth by testing reality, via asserts.
def test_assert_truth
  assert false                # This should be true

Change the false to true and re-run the test. After you are done, think about what you are learning. In this case, ignore everything except the method name (test_assert_truth) and the parts inside the method (everything before the end).

In this case the goal is for you to see that if you pass a value to the assert method, it will either ensure it is true and continue on, or fail if the statement is false.

Running the Koans automatically

This section is optional.

Normally the path to enlightenment looks like this:

cd ruby_koans
# edit
# edit
# etc

If you prefer, you can keep the koans running in the background so that after you make a change in your editor, the koans will immediately run again. This will hopefully keep your focus on learning Ruby instead of on the command line.

Install the Ruby gem (library) called observr and then ask it to “watch” the koans for changes:

cd ruby_koans
# decide to run rake automatically from now on as you edit
gem install observr
observr ./koans/koans.watchr


A special thanks to Mike Clark and Ara Howard for inspiring this project. Mike Clark wrote an excellent blog post about learning Ruby through unit testing. This sparked an idea that has taken a bit to solidify, that of bringing new rubyists into the community through testing. Ara Howard then gave us the idea for the Koans in his ruby quiz entry on Meta Koans (a must for any rubyist wanting to improve their skills). Also, “The Little Lisper” taught us all the value of the short questions/simple answers style of learning.

Mike Clark's post

Meta Koans

The Little Lisper

Other Resources

The Ruby Language

Try Ruby in your browser

Dave Thomas' introduction to Ruby Programming Ruby (the Pick Axe)

Brian Marick's fantastic guide for beginners Everyday Scripting with Ruby

Other stuff


Jim Weirich <>


Joe O'Brien <>

Issue Tracker


Ruby 1.8.x or later and Rake (any recent version)


RubyKoans is released under a Creative Commons, Attribution-NonCommercial-ShareAlike, Version 3.0 ( License.


Learn Ruby with the Edgecase Ruby Koans






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