GitHub Repos

Sadly by necessity some of my repos are private. Those that are private are clearly marked. For those that are, please don’t ask me to share the code, because I can’t. They’re listed here purely for my reference.

Ruby katas

See below for a quick start guide if writing a kata from scratch

  • Bowling kata - bowling kata implemented in Ruby
    • Note that the bowling kata can sometimes be a bit opaque (because if you don’t play the game, the scoring is quite complex), but I’ve updated the readme on the Made Tech site to have a simpler explanation (in case that gets lost, I’ve also added it to the readme in my repo)
  • bowling kata as a Ruby gem (csud-bowl-kata) - bowling kata designed to be released as a Ruby gem (might not actually be on yet)
  • tic-tac-toe kata - tic-tac-toe kata implemented in Ruby
  • wordwrap kata - wordwrap kata implemented in Ruby
  • Mars Rover kata

Quick start Ruby kata guide

  • Create dedicated folder
  • Create git repo
  • Check you have ruby installed - which ruby
  • bundle init
  • bundle add rspec
    • Or just add gem 'rspec' to end of gemfile
    • And then bundle install –path ‘vendor/bundle’
    • and rspec --init
  • Create a spec folder (might have already been done when you ran rspec --init) and a spec file, eg fizzbuzz_spec.rb
  • Now bundle exec rspec
  • Create something like fizzbuzz.rb to contain the code under test - can stick it in root
    • For first demo you might want to put executable code into spec file
    • Then refactor to put code in fizzbuzz.rb
  • Test file will have require 'rspec' and require './fizzbuzz' at the top
    • And subject = to call system under test
  • See this commit for an example

Tutorials and Guides


Using Sinatra to build a web api

Deployment with Heroku


Debugging on command line

Debugging in VS Code using Ruby extension and ruby-debug-ide

Step by step guide to get started

  • First, on the command line:
  • sudo gem install debase
  • gem install ruby-debug-ide
  • Now, in the same folder:
  • rdebug-ide app.rb (If necessary, replace app.rb with the appropriate path and file name to start up the code you want to debug).
  • Open up VS Code.
  • Click the Play button with a bug icon over on the left, then click “Create a launch.son file” (if you don’t already have one): Run Debug button
  • When it asks you to Select Environment, select Ruby.
  • Select “Listen for rdebug-ide”.
  • Set a breakpoint in one of your files, eg in your default ‘/’ route in app.rb for a Sinatra web app.
  • Click the green run triangle next to the dropdown top left.
  • If what you’re running is a webapp, visit the app in the browser (eg http://localhost:4567 for a Sinatra app where you put your breakpoint in the ‘/’ route).
  • You should now hit your breakpoint.

Once you’re up and running - an example

  • I currently have this working in my bowling-kata-ruby repo:
    • Checkout this commit
    • Run rdebug-ide src/bowling_cli.rb on the command line
    • Select “Listen for rdebug-ide” in the dropdown top left
    • Set a breakpoint, for instance in bowling_cli.rb
    • Click the green run triangle next to the dropdown top left

Debugging rspec tests

  • If you want to debug Rspec tests, follow the guide above, then when click the Run Debug button, select Add configuration from the dropdown and add configs for "RSpec - active spec file only" and "RSpec - all"

More info

  • Original article here: Debugging Ruby with breakpoints in VS Code (scroll down to where it talks about VS Code)
    • !! Note that when it says to add a launch.json and “open the debugging tab”, you need to follow the instructions here (I suspect the UI has changed a little since that article was written)
    • Then when you are told to add a configuration, you need to select Ruby and then select Listen for rdebug-ide. This will have the effect of adding a new entry into the "configurations" section of your launch.json that looks something like this:
          "name": "Listen for rdebug-ide",
          "type": "Ruby",
          "request": "attach",
          "remoteHost": "",
          "remotePort": "1234",
          "remoteWorkspaceRoot": "${workspaceRoot}"
  • Note that you can do the same for Rspec by selecting Add configuration and adding in configs for "RSpec - active spec file only" and "RSpec - all"
  • Also note that if you get any errors, you might have to restart the debug server with rdebug-ide --host --port 1234 --dispatcher-port 26162 /path/to/file.rb
  • I got an ECONNREFUSED error on Windows but I think this was either because I hadn’t restarted all instances of VS Code or because I was passing the wrong file name to the rdebug-ide command
  • I also had another problem that I started debugging and it seemed like it hung, but this was because I was running code that was asking for command line input, which I wasn’t providing.
  • I haven’t managed to work out how to pass command line arguments to code that you’re debugging.

Debugging in VS Code using ruby-debug extension

  • Article here
  • I didn’t get this working on Windows or Mac, but didn’t spend so long on Mac.

Gems, packaging, versioning


Front end testing

In spec_helper.rb:

require "rspec-html-matchers"
RSpec.configure do |config|
  config.include RSpecHtmlMatchers

In Gemfile:

gem "rspec-html-matchers"


Test cases in rspec

You can handle test cases in rspec in the way shown below - and there are more examples here. Below we use a hash to map inputs (“rolls”) to outputs “scores”, and then use an each statement to loop through the list of elements in the hash.

expected_scores_with_a_strike_in_the_tenth_frame = {
        "44 44 44 44 44 44 44 44 44 X 32" => (9*8) + (10+3+2),
        "44 44 44 44 44 44 44 44 44 X X-" => (9*8) + (10+10+0),
        "44 44 44 44 44 44 44 44 44 X -X" => (9*8) + (10+0+10),
        "44 44 44 44 44 44 44 44 44 X XX" => (9*8) + (10+10+10),
        "44 44 44 44 44 44 44 44 44 X 46" => (9*8) + (10+4+6),
        "44 44 44 44 44 44 44 44 44 X 6-" => (9*8) + (10+6+0),
        "44 44 44 44 44 44 44 44 44 X -3" => (9*8) + (10+0+3),
        "44 44 44 44 44 44 44 44 44 X --" => (9*8) + (10+0+0),
        "44 44 44 44 44 44 44 44 44 X 2-" => (9*8) + (10+2+0),
        "44 44 44 44 44 44 44 44 44 X -5" => (9*8) + (10+0+5)
    expected_scores_with_a_strike_in_the_tenth_frame.each do |rolls, score|
        it "adds the final two rolls to the score twice, when a strike is rolled in the final frame: '#{rolls}'" do
            bowling =            
            expect(bowling.score(rolls)).to eq(score)

Testing command-line inputs and outputs (stdin, stdout, stderr)

You can stub command-line inputs using standard rspec stubbing functionality and the fact that gets and puts are functions inherited from Object by all classes. Note that you can also mimic several repeated inputs by giving a comma-separated list. Note that in the examples below, @communicator and @mars_rover_app are classes written by me, and I am specifying their inputs and outputs.

For the code below you will need the rspec and rspec-html-matchers gems in your Gemfile (see example here).

allow(@communicator).to receive(:gets).and_return(INITIAL_INPUT, "f", "r", "f", "f", "l", "b", "") 

You can test whether what you expected got sent to stdout or stderr using the to output functionality:

expect{@mars_rover_app.start}.to output(a_string_ending_with(MarsRoverApp::BAD_INPUT_ERROR)).to_stdout

Note that you can use matchers such as a_string_ending_with, a_string_starting_with, and a_string_including so that you are only checking a subset of the output rather than everything that has been sent to stdout. More matchers listed here.

More examples of stdin and stdout testing in this file here.

Language Features

Misc Language Stuff

  • General Ruby docs (they’re pretty good, once you’ve searched for what you’re interested in).
  • Return values in Ruby functions are the last thing that was assigned
    • the return statement is often not used
  • IRB is the standard Ruby repl (run irb on command line)
    • If you run it using irb -rpp, you’ll get pretty-printing (passing -r to irb will automatically require a library when irb is loaded - in this case the pretty_print library).
    • Enter exit to leave)
    • Enter load './myfile.rb' to load a Ruby file called myfile.rb in the current folder (./)
      • To reload, just enter load './myfile.rb' again.
    • An alternative to IRB is this handy online repl tool
  • The puts statement is how you can output to console - useful for quick-and-dirty debug logging.

    • If you want to get the output from something in a Ruby script onto the command line and into a pipe: Use the puts keyword in the Ruby script

    • If Chef, you can use knife exec and then pipe the output to other commands

    • Otherwise just run the script with the script name, and pipe straight to something else

  • Boolean methods should be suffixed with a question mark. More here. However this is a convention and is not enforced. It’s possible to write a function suffixed with a question mark that doesn’t return a bool. In fact it’s really used to indicate that the function is asking a question - the answer might not be a bool in practice. More here.

  • Methods that end in ! indicate that the method will modify the object it’s called on. Ruby calls these “dangerous methods” because they change state that someone else might have a reference to.

  • Calling javascript code from Ruby:

  • Static methods and the self keyword

  • Frozen values: Frozen strings

  • Calling javascript code from Ruby:

  • Calling an API or a url - notes summarised from here
    • You’ll need to require json and net/http. The Net::HTTP Ruby library will give you some methods to help you send an HTTP request and the JSON library will help you to parse any JSON data that comes back
    • Use the following code to make a request to an API and parse the JSON that is returned. Note that endpoint will contain the url of the API, as a string:
uri = URI.parse(URI.encode(endpoint))
api_response = Net::HTTP.get(uri)
    • You can use HEREDOC for multi-line string literals, instead of concatenating individual lines.
    • Instead of this…
            populated_grid = 
            "-------------\n" +
            "|     | 360 |\n" +
            "|     | ^^^ |\n" +
            "|     | TST |\n" +
  • … you can do this:
            populated_grid = 
            |     | 360 |
            |     | ^^^ |
            |     | TST |

Blocks / anonymous functions, and the yield keyword

  • Blocks of code, aka anonymous or unnamed functions
    • { |i| puts 2**i } is equivalent to do |i| puts 2**i end
    • ie do and end take the place of the opening and closing braces in defining a block of code.
    • Therefore (1..5).each { |i| puts 2**i } is equivalent to
(1..5).each do |i|
   puts 2**i
  • What we’re seeing in this example is that each is a method that takes a block of code as a parameter.
  • What’s not quite so obvious is that in this case, the block of code is an anonymous function that takes a parameter. The parameter is named i and is indicated by surrounding it with pipes: |i|
  • See yield below for more on blocks, and blocks that take parameters.

  • yield keyword: yield is a keyword in Ruby that calls a block that was given to a method.
    • Whenever you pass a block to a method (such as each, collect, select, and so on) this method can then call the block by using the keyword yield.
    • There are a couple of examples of its usage in my Mars Rover app code base, including this one.
      • I did previously have a nested yield here (the handle_exceptions method uses yield to forward a block to AppHelper.handle_mars_rover_exceptions, which also uses yield), but I refactored it out here because it represented unnecessary complexity.
    • So, in a Sinatra layout template, <%= yield %> marks the place where the other template (the one that is being wrapped) is supposed to be inserted. Example here.
    • Every Ruby method can take a block as a parameter
      • We can invoke that block using the yield keyword.
        • The block won’t get evaluated until the yield keyword appears.
      • So, in the following example, although we don’t explicitly declare that the sandwich function takes a block as a parameter, we see that it can because of its use of the yield keyword. First we define the sandwich function and then we call it and pass a do .. end block to it. The output is also shown.
# blocks.rb
def sandwich
    puts "top bread"
    puts "bottom bread"
sandwich do
    puts "mutton, lettuce, and tomato"

ruby yield

  • So what about yielding a block with a parameter? Remember we can define a block with a param like this:
do |markup|
  puts markup
  • The code above defines a block that takes a parameter called markup, then just outputs that markup to the command line.
  • So let’s define a function that can take that block of code as a parameter and then call it using yield:
def tag(tagname, text)
  html = "<#{tagname}>#{text}</#{tagname}>"
  yield html
  • The above code takes a tagname and text and uses string interpolation to turn it into a chunk of html. Then the statement yield html is saying “Call the block of code that has been passed in, and pass html to it as an argument.”
  • So finally we can call the tag function and pass in our original block of code so that the tag function can * call* our original block:
tag("p", "Lorem ipsum dolor sit amet") do |markup|
  puts markup
  • The result of the above call to tag will be the following being output to the command line:
    • gcam “<p>Lorem ipsum dolor sit amet</p>



  • Also known as associative arrays.
  • Some examples of hashes:
    my_hash =
    my_hash["one"] = "First element"
    my_hash2 = {}
    my_hash2[:one] = "First element"
    my_hash3 = { "first_name" => "Pippi", "last_name" => "Longstocking" }
    my_hash4 = { :first_name => "Pippi", :last_name => "Longstocking" }
    # this is equivalent to the above:
    my_hash4 = { first_name: "Pippi", last_name: "Longstocking" }
  • :name is a symbol (see below)
  • The => operator is called a “hashrocket”.
  • when hashes have string keys, those strings are frozen
  • Ruby documentation on hashes (it’s pretty good documentation)
  • Using an array as a key in your hash
    • we thought about creating an example in our wordwrap academy kata, but instead we used a nested hash as a key


  • Negative indices:
    • To get last array element, use negative index: [-1]
    • The second-to-last element has index -2, and so on.
  • Square brackets are built-in constructors, but you can also use the new keyword if you want: a = is equivalent to a = []
  • Adding elements to arrays can be done in two ways:
    • a[0] = "A"
    • a << "A"


  • gsub: Find and replace
  • Frozen strings
  • String interpolation. Do it like this: “search/#{type}”, where type is a variable
    • !! It only works in double quotes!
    • In fact it’s not recommended to use ‘ in ruby. Use “ instead.
    • It doesn’t seem to work in a Ruby script run via knife exec - instead, you can do this:
      • This: query=”fqdn:”+ARGV[2]
    • See below for how to do string interpolation with symbols
  • Single-quoted strings
    • Single-quoted strings are literal strings. You can’t do interpolation with them but you can include special characters without having to escape them - so they can be useful for that. More here.
  • ?h is the same as "h"
  • Double and single quotes are built-in constructors, but you can also use the new keyword if you want: s ="A man, a plan, a canal—Panama!")


  • Symbols are things that look like this :symbol

    • The closest thing in C# is an enum

    • The symbol itself is the value - they are not variables and you don’t assign to them

    • Symbols do hold strings of characters, they are just immutable

    • This means that when you reference a symbol in string interpolation, what is printed out will be the name of the symbol

    • So #{:node} will give node as the output

  • A variable that has a string as its value will be mutable, but a symbol is immutable, and stored in a single place in memory

Dates and Times

  • Time is a built-in class
    • you have to use require 'time'
  • now = will give you the current time
    • now = is equivalent
  • or you can initialise: moon_landing =, 7, 20, 20, 17, 40) (= 1969-07-20 20:17:40)
  • By default, Time uses the local time zone, but this introduces weird location-dependence to the operations, so it’s a good practice to use UTC instead: moon_landing = Time.utc(1969, 7, 20, 20, 17, 40)
  • Other useful Time methods:
    • now.year (= 2020)
    • now.month (= 12)
    • (= 31)
    • now.hour (= 19)
    • now = ()
    • now.wday (= 0 for Sunday)
    • Date::DAYNAMES[] (= SUNDAY)
      • you have to use require 'date'
    • Date.parse("10/10/2010")
    • Date.parse("September 3")
      • More on date parsing here


  • Functions are not attached to objects


  • Methods are functions attached to objects
  • This notation - String#include? indicates a method called include? which is a String instance method.

Methods and functions

  • You don’t need brackets when passing arguments to methods and functions (they’re optional) - you can use spaces instead.

Command Line Input


  • great article here on inheritance in Ruby - includes an explanation of why instance variables are not defined by classes and are therefore also not inherited by subclasses.

Division and other Maths

  • By default, the / operator does integer division - so 2/3 = 0
    • If you want floating point division, add .0 to one of your integers: 2/3.0
  • To get “to the power of”, use ** instead of ^
    • 2**3 = 8
  • More complex Maths operations are available via the Math module
    • Math.log10(10) means “10 to the power what equals 10?” and the answer is “1”.
    • Maths.log(10) is used for ln or the natural logarithm (log to the base e)
    • Math::E is used for e
    • Math::PI is pi and is an example of a module constant
    • Also available:
      • Math.sqrt(4) (answer = 2)
      • Math.cos(2*Math::PI) (answer = 1)


  • If RSpec is a Gem, why is it never required in your spec files? How do they get the code they need? And what does the -- mean in front of require spec_helper in the .rspec file?

Monkey patching

“It’s simply the dynamic replacement of attributes at runtime.

For instance, consider a class that has a method get_data. This method does an external lookup (on a database or web API, for example), and various other methods in the class call it. However, in a unit test, you don’t want to depend on the external data source - so you dynamically replace the get_data method with a stub that returns some fixed data.”

From here.

Caution: “In our experience, having monkey-patched gems is usually one of the hardest things to deal with. We have to spend hours updating monkey-patched gems to make them compatible with newer Rails APIs. So please keep that in mind before monkey patching Rails core libraries or gems that depend on specific Rails versions.” From here.


See the Ruby Gems page for most Ruby Troubleshooting stuff (including getting Ruby working on a 2022 Macbook)

Database stuff

  • For Ruby, PostgreSQL, Sinatra/Rails and heroku see here