This document discusses Ruby gems, including: - How to interact with gems using the gem command to search, install, uninstall, list, and view documentation for gems. - The standard structure for gems including code, tests, documentation, and a gemspec file. - How to create your own gem including naming conventions, building a gemspec, and publishing the gem to RubyGems.org.

1. Deepak H B
Full-Stack Developer
Gmail: deepakhb2@gmail.com
Linkedin: http://in.linkedin.com/in/deepakhb
GitHub: https://github.com/deepakhb2

2. Ruby Gems

3. Introduction
• The gem command allows you to interact with RubyGems.
• Finding Gems
$gem search rails
• To find more info on gems
$gem search rails –d
• The install command downloads and installs the gem and any necessary
dependencies then builds documentation for the installed gems.
$gem install rails
• The list of installed gems can be viewed by running following command
$gem list
• Uninstallin gems
$gem uninstall rails
• If you uninstall a dependency of a gem, RubyGems will ask for
confirmation before uninstalling.
• The documents can be viewed by using ri.
$ri RBTree
• You can view the documentation for your installed gem in your browser
with server command
$gem server

4. Structure of Gem
• Each gem has name version and platform
• RubyGems platform is ruby, which means it works on
any platform Ruby runs on.
Compnents of Ruby gems
• Code
• Documentation
• Gemspec

5. Contd..
• Each gem follows the same standard structure of
code organization
freewill/
├── bin/
│ └── freewill
├── lib/
│ └── freewill.rb
├── test/
│ └── test_freewill.rb
├── README
├── Rakefile
└── freewill.gemspec

6. Contd..
• The lib directory contains the code for the gem
• The test or spec directory contains tests, depending on
which test framework the developer uses.
• The gem usually has a Rakefile. Which the rake program
used to automate tests, generate code and perform other
tasks.
• Documentation is usally included in the README and inline
with the code.
• The final piece is the gemspec, which contains the
information about the gem.

7. Contd..
% cat freewill.gemspec
Gem::Specification.new do |s|
s.name = 'freewill‘
s.version = '1.0.0'
s.summary = "Freewill!"
s.description = "I will choose Freewill!"
s.authors = ["Nick Quaranto"]
s.email = 'nick@quaran.to‘
s.homepage = 'http://example.com/freewill'
s.files = ["lib/freewill.rb", ...]
end

8. Making your own gem
• Creating publishing your own gem is simple thanks to the tools baked
right into RubyGems.
• Create the folder containing hello.gemspec, lib and lib/hello.rb
• The code for your package is placed inside lib.
• The code inside of lib/hello.rb is pretty bare bones.
$cat lib/hello.rb
• The content for gemspec needs to be updated.
• After you have created gemspec , you can build the gem from it.
gem build hello.gemspec
• Then you can install the generated gem locally to test it out.
• This gem can be pushed to to ruby gems by running following command.
Gem push hello-0.0.0.gem

9. Name your gem
Gem name Require statement Main class or module
fancy_require require 'fancy_require' FancyRequire
ruby_parser require 'ruby_parser' RubyParser
net-http-persistent require
'net/http/persistent' Net::HTTP::Persistent
rdoc-data require 'rdoc/data' RDoc::Data
autotest-growl require 'autotest/growl' Autotest::Growl
net-http-digest_auth require
'net/http/digest_auth' Net::HTTP::DigestAuth

10. Contd..
• If you publish a gem on rubygems.org it may be removed if the
name is objectionalble, violates intellectual property or the
contents of the gem meet these criteria.
• You can also report such a gem on the RugyGems support site.
• Don’t use upper case letters.
• Use underscore for multiple words
– If a class or module has multiple words, use underscores to
separate them.
– This matches the file the user will require, making is easier for
the use to start using your gem.

11. Contd..
• Mix underscore and dashes appropriately.
– If your class or module has multiple words and your also adding
functionality to another gem, follow both of the rules above.
– Example, “net-http-digest_auth adds HTTP digest authentication
to net/http.
– The user will require “net/http/digest_aut” to use the extension
“Net::HTTP::DigestAuth.
• Use dashes for extensions.
– If your adding functionality to another gem, use a dash.
– This usually correspond to a / in the require statement and :: in
the name of your main class or module

12. Publishing to RubyGems.org
• The simplest way to distribute a gem for public consumption is to
use RubyGems.org.
• Gems that are published to RubyGems.org can be installed via the
gem install command.
• To begin, you will need to create an account on RubyGems.org.
• After creating the account, use your email and password when
pushing the gem.
• RubyGems saves the credentials in ~/.gem/credentials for you so
you only need to log in once.