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Make your own gem |
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From start to finish, learn how to package your Ruby code in a gem. This guide has several parts, jump to any here:
- Intro
- Your first gem
- Requiring more files
- Adding an executable
- Writing tests
- Documenting your code
- Wrapup
Creating and publishing your own gem is simple thanks to the tools baked right into RubyGems. Let’s make a simple “hello world” gem, and feel free to play along at home! The code for the gem we're going to make here is up on GitHub.
I started with just one Ruby file for my hola gem, and the gemspec.
You'll need a new name for yours (maybe hola_yourusername) to publish it. By
the way, there's some basic
recommendations to follow
for naming a gem.
% tree
.
├── hola.gemspec
└── lib
└── hola.rb
Code for your package is placed within the lib directory. The convention is
to have one Ruby file with the same name as your gem, since that gets
loaded when require 'hola' is run. That one file is in charge of setting up
your gem's code and API.
The code inside of lib/hola.rb is pretty bare bones, we just want to see some
output.
% cat lib/hola.rb
class Hola
def self.hi
puts "Hello world!"
end
end
The gemspec defines what’s in the gem, who made it, and the version of the gem. It’s also your interface to RubyGems.org. All of the information you see on a gem page (like jekyll’s) comes from the gemspec.
% cat hola.gemspec
Gem::Specification.new do |s|
s.name = 'hola'
s.version = '0.0.0'
s.date = '2010-04-28'
s.summary = "Hola!"
s.description = "A simple hello world gem"
s.authors = ["Nick Quaranto"]
s.email = 'nick@quaran.to'
s.files = ["lib/hola.rb"]
s.homepage =
'http://rubygems.org/gems/hola'
end
Look familiar? The gemspec is also Ruby, so you could wrap scripts to generate the file names and bump the version number. There are lots of fields the gemspec can contain, to see them all check out the full reference.
Once we have our gemspec, we can build a gem from it. We can then install it locally to test it out.
% gem build hola.gemspec
Successfully built RubyGem
Name: hola
Version: 0.0.0
File: hola-0.0.0.gem
% gem install ./hola-0.0.0.gem
Successfully installed hola-0.0.0
1 gem installed
Of course, our smoke test isn’t over yet: Let’s require our gem and use it!
% irb -rubygems
>> require 'hola'
=> true
>> Hola.hi
Hello world!
Hola now needs to be shared with the rest of the Ruby community. Publishing your gem out to RubyGems.org only takes one command, granted you have an account on the site. Once you’re signed up, then you can push out a gem.
% gem push hola-0.0.0.gem
Enter your RubyGems.org credentials.
Don't have an account yet? Create one at http://rubygems.org/sign_up
Email: nick@quaran.to
Password:
Signed in.
Pushing gem to RubyGems.org...
Successfully registered gem: hola (0.0.0)
In just a few moments (usually a minute), your gem will be available for installation by anyone.
% gem list -r hola
*** REMOTE GEMS ***
hola (0.0.0)
% gem install hola
Successfully installed hola-0.0.0
1 gem installed
It’s really that easy to share code with Ruby and RubyGems.
Having everything in one file doesn't scale well. Let's add some more code to this gem.
% cat lib/hola.rb
class Hola
def self.hi(language = "english")
translator = Translator.new(language)
puts translator.hi
end
end
class Hola::Translator
def initialize(language)
@language = language
end
def hi
case @language
when "spanish"
"hola mundo"
else
"hello world"
end
end
end
This file is getting pretty crowded. Let's break out the Translator into a
separate file. As mentioned before, the gem's root file is in charge of
loading code for the gem. The other files for a gem are usually placed in a
directory of the same name of the gem inside of lib. We can split this gem
out like so:
% tree
.
├── hola.gemspec
└── lib
├── hola
│ └── translator.rb
└── hola.rb
The Translator is now in lib/hola, which can easily be picked up with a
require statement from lib/hola.rb. The code for the Translator did not
change much:
% cat lib/hola/translator.rb
class Hola::Translator
def initialize(language)
@language = language
end
def hi
case @language
when :spanish
"hola mundo"
else
"hello world"
end
end
end
But now our hola.rb file has some code to load the Translator:
% cat lib/hola.rb
class Hola
def self.hi(language = :english)
translator = Translator.new(language)
translator.hi
end
end
require 'hola/translator'
Let's try this out. First, fire up irb!
% irb -Ilib -rhola
irb(main):001:0> Hola.hi(:english)
=> "hello world"
irb(main):002:0> Hola.hi(:spanish)
=> "hola mundo"
Why did we specify -Ilib? Well, in order to use the local version of our gem
we need to add to the $LOAD_PATH with -I. We could have done this inside of
our gem but that's considered a bad pattern for gems. There's many more anti-patterns
(and good patterns!) for gems, explained in this guide.
If you've added more files to your gem, make sure to remember to add them to
your gemspec's files array before publishing a new gem! For this reason
alone, many developers use automation tools like
Hoe,
Jeweler, or just plain old
Rake to generate
the gemspec.
Adding more directories with more code from here is pretty much the same process. Split your Ruby files up when it makes sense! Making a sane order for your project will help you and your future maintainers from headaches down the line.
Gems not only provide libraries of code, but they can also expose one or many
executable files to your shell's PATH. Probably the best known example of
this is rake. Another very useful one is prettify_json.rb, which comes
with the JSON gem, which formats JSON in a
readable manner (and is included with Ruby 1.9). Here's an example:
% curl -s http://jsonip.com/ | \
prettify_json.rb
{
"ip": "24.60.248.134"
}
Adding executables is a simple process, you just need a file in bin, and set
it in the gemspec. Let's add one for the Hola gem. First let's add the file
and make it executable:
% mkdir bin
% touch bin/hola
% chmod a+x bin/hola
The executable file itself just needs a shebang in order to figure out what program to run it with. Here's what Hola's executable looks like:
% cat bin/hola
#!/usr/bin/env ruby
require 'hola'
puts Hola.hi(ARGV[0])
All it's doing is loading up the gem, and passing the first command line argument as the language to say hello with. Here's an example of running it:
% ruby -Ilib ./bin/hola
hello world
% ruby -Ilib ./bin/hola spanish
hola mundo
There's another strange command line flag here: -Ilib. Usually RubyGems
includes the lib directory for us, and it will for gem executables. However,
if we're running it outside of RubyGems, we have to bring it in ourselves.
Finally, to get Hola's executable included when we push the gem, you'll need to add it in the gemspec.
% head -4 hola.gemspec
Gem::Specification.new do |s|
s.name = 'hola'
s.version = '0.0.1'
s.executables << 'hola'
Push up that new gem, and you'll have your own command line utility published!
You can add more executables as well in the bin directory if you need to,
there's an executables array field on the gemspec.
Testing your gem is extremely important. Not only does it help assure you that your code works, but it helps others know your gem does its job. When evaluating a gem, Ruby developers tend to place a test suite (or lack thereof) as one of the main reasons for trusting that piece of code.
Gems support adding test files into the package itself so tests can be run when a gem is downloaded. An entire community effort has sprung up called GemTesters to help document how gem test suites run on different architectures and interpreters of Ruby.
In short: TEST YOUR GEM! Please!
Test::Unit is Ruby's built-in test framework. There are
lots of
tutorials for
using it online. There's many other test frameworks available for Ruby as
well, RSpec is a popular choice. At the end of the day,
it doesn't matter what you use, just TEST!
Let's add some tests to Hola. We've got a few more files now, namely a
Rakefile and a brand new test directory.
% tree
.
├── Rakefile
├── bin
│ └── hola
├── hola.gemspec
├── lib
│ ├── hola
│ │ └── translator.rb
│ └── hola.rb
└── test
└── test_hola.rb
Our Rakefile gives us some simple automation for running tests.
% cat Rakefile
require 'rake/testtask'
Rake::TestTask.new do |t|
t.libs << 'test'
end
desc "Run tests"
task :default => :test
Now we can run rake test or simply just rake to run tests. Woot! Here's
what my basic test file looks like.
% cat test/test_hola.rb
require 'test/unit'
require 'hola'
class HolaTest < Test::Unit::TestCase
def test_english_hello
assert_equal "hello world",
Hola.hi("english")
end
def test_any_hello
assert_equal "hello world",
Hola.hi("ruby")
end
def test_spanish_hello
assert_equal "hola mundo",
Hola.hi("spanish")
end
end
Finally, to run the test:
% rake test
(in /Users/qrush/Dev/ruby/hola)
Loaded suite
Started
...
Finished in 0.000736 seconds.
3 tests, 3 assertions, 0 failures, 0 errors, 0 skips
Test run options: --seed 15331
It's green! Well, depending on your shell colors. For more great examples, the best thing you can do is hunt around GitHub and read some code.
By default most gems use RDoc to generate docs. There's a lot of great tutorials for learning how to mark up your code with RDoc. Here's a simple example:
# The main Hola driver
class Hola
# Say hi to the world!
#
# Example:
# >> Hola.hi("spanish")
# => hola mundo
#
# Arguments:
# language: (String)
def self.hi(language = "english")
translator = Translator.new(language)
puts translator.hi
end
end
Another great option for documentation is YARD, since when you push a gem, RubyDoc.info generates YARDocs automatically from your gem. YARD is backwards compatible with RDoc, and it has a good introduction on what's different and how to use it.
With this basic understanding of building your own RubyGem, we hope you'll be on your way to making your own! The next few guides cover patterns in making a gem and the other capabilities of the RubyGems system.
This tutorial was adapted from Gem Sawyer, Modern Day Ruby Warrior. The code for this gem can be found on GitHub.