RubyGems Explained: Installing And Managing Ruby Libraries

RubyGems

The official package manager for Ruby is called RubyGems. The term “gems” refers to software programs that are distributed through this method. A standardized framework for packaging, installing, updating, and uninstalling Ruby libraries and applications is offered by RubyGems. Both users and developers can benefit from its standardized package structure, central repository (often hosted on rubyforge.org), end-user administration tools (such as the gem command), and ability to install and manage several concurrently installed versions of the same library.

Using the gem Command Line Tool

The gem command-line script serves as the main interface for working with the RubyGems system.

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Installation and Management

There are several things you can do from the command line with gem subcommands:

Installing a Gem: Use gem install to install a gem’s most recent version. The gem install command will download and install dependencies automatically if a gem has any, particularly if the --include-dependencies parameter is set.

Specifying a Version for Installation: Version requirements, such as supplying the version number using the --version parameter, can be used during installation.

Listing Gems: You can use gem list to list installed gems or gem query to query local repositories. Additionally, you can search external repositories for gems that are available.

Updating and Uninstalling:

• To update a specific gem (or all gems): gem update [gemname].
• To remove a gem: gem uninstall [gemname].

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Integrating Gems into Ruby Code

The require method is usually used to use a gem inside a Ruby program.

Loading Gems (Ruby Version Specifics)

Ruby 1.8: Gem-using programs must explicitly require 'rubygems' before any other require statements for gem-installed libraries if you’re running Ruby 1.8. When the rubygems module is loaded, the default need method is modified to search the paths containing installed gems.

Ruby 1.9 and Later: Requiring "rubygems" is typically not required because the rubygems module is part of the standard library in Ruby 1.9 and the Ruby interpreter is designed to automatically detect installed gems.

Specifying Dependencies in Code

Kernel#require_gem is a useful tool for making sure your program only executes when a particular version of a gem is available. This function serves as an assertion, and if the necessary version requirement is not satisfied, it will raise a Gem::LoadError.

Requiring a Minimum Version

Using the Pessimistic Operator (~>): The ~> comparison operator allows any revision number (e.g., ~> 2.0 matches 2.0.1, 2.0.20), but it limits a gem to a certain minor version. When a particular API version is needed, this is helpful.

Checking for a Gem’s Presence: You can check if a required gem is installed from within your code using the Gem::Specification.find_by_name method:

Packaging Your Code as a Gem

Your Ruby application or library is packaged as a gem if you want to distribute it.

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The Gemspec File

Creating a gem starts with writing a specification file, or gemspec (e.g., <gem name>.gemspec), which contains the necessary metadata.

Required attributes for a Gem::Specification include:

• Name
• summary
• version
• files (an array containing a list of all the files to be included)

# shielding.gemspec
require 'rubygems'

spec = Gem::Specification.new do |s|
  s.name        = 'shielding'
  s.summary     = 'A library for calculating the strength of duophasic shielding'
  s.author      = 'Bob Zaff'
  s.version     = '1.0.0'
  s.files       = Dir['lib/*.rb'] # All Ruby files under the lib directory
end

# Print gem info to confirm
puts "Gem name: #{spec.name}"
puts "Version: #{spec.version}"
puts "Author: #{spec.author}"
puts "Files included: #{spec.files.join(', ')}"

Output

Gem name: shielding
Version: 1.0.0
Author: Bob Zaff
Files included: 

Adding Dependencies: If your gem depends on another gem, you use add_dependency to specify that dependency in the gemspec.

spec.add_dependency('another_gem')              # Any version will do.
spec.add_dependency('yet_another_gem', '~> 3.0') # Must be 3.0.x series.

Building and Distributing

You can use the command line to create the gem file (.gem) after the gemspec has been defined:

$ gem build shielding.gemspec
Attempting to build gem spec 'shielding.gemspec'
Successfully built RubyGem
Name: shielding
Version: 1.0.0
File: shielding-1.0.0.gem

The resulting .gem file can then be installed locally or uploaded to a central repository (like RubyForge) for others to find and install remotely.

If the Ruby ecosystem may be compared to a vast library, RubyGems serves as the mechanism for cataloguing and distribution. The gem tool is your handy librarian; it allows you to find new resources (gems or libraries), install them, and manage the documentation (versions and dependencies) so that you have everything you need when you start working.

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