As with most programming languages, Ruby leverages a wide set of third-party
libraries.
{: .summary}

Nearly all of these libraries are released in the form of a **gem**,
a packaged library or application that can be installed with a tool
called [**RubyGems**][1].

RubyGems is a Ruby packaging system designed to facilitate the creation,
sharing and installation of libraries (in some ways, it is a distribution
packaging system similar to, say, `apt-get`, but targeted at Ruby software).
Ruby comes with RubyGems by default since version 1.9, previous
Ruby versions require RubyGems to be [installed by hand][2].

Some other libraries are released as archived (.zip or .tar.gz)
directories of **source code**. Installation processes may vary,
typically a `README` or `INSTALL` file is available with instructions.

Let’s take a look at finding libraries and installing them for your own
use.

### Finding libraries

The main place where libraries are hosted is [**RubyGems.org**][1], a public
repository of gems that can be searched and installed onto your machine.
You may browse and search for gems using the RubyGems website,
or use the `gem` command.

Using `gem search -r`, you can search RubyGems' repository. For
instance, `gem search -r rails` will return a list of Rails-related
gems. With the `--local` (`-l`) option, you would perform a local search
through your installed gems. To install a gem, use `gem install [gem]`.
Browsing installed gems is done with `gem list`. For more
information about the `gem` command, see below or head to
[RubyGems’ docs][3].

There are other sources of libraries though.
[**GitHub**][5] is the main Ruby-related content repository.
Most often a gem source code will be hosted on GitHub while being
published as a fully-fledged gem to RubyGems.org.

[**The Ruby Toolbox**][6] is a project that makes it easy to explore open
source Ruby projects. It has categories for various common development tasks,
collects a lot of information about the projects like release and commit
activity or dependencies and rates projects based on their popularity on
RubyGems.org and GitHub. This makes it easy to find a gem which solves
a particular problem such as web frameworks, documentation tools and
code quality libraries.

### A few more words about RubyGems

Here is a quick review of the `gem` command for your daily use.
[More detailed documentation][7] is available, covering all aspects
of this packaging system.

#### Searching among available gems

The **search** command can be used to look for gems, based on a string.
Gems which names start with the specified string will be listed in return.
For instance, to search for the “html”-related gems:

<figure class="highlight"><pre><code class="language-sh" data-lang="sh"><span class="nv">$ </span>gem search <span class="nt">-r</span> html

<span class="k">***</span> REMOTE GEMS <span class="k">***</span>

html-sample <span class="o">(</span>1.0, 1.1<span class="o">)</span></code></pre></figure>

The `--remote` / `-r` flag indicates that we want to inspect the
official RubyGems.org repository (default behaviour).
With the `--local` / `-l` flag you would perform a local search
among your installed gems.

#### Installing a gem

Once you know which gem you would like to **install**, for instance the
popular Ruby on Rails framework:

<figure class="highlight"><pre><code class="language-sh" data-lang="sh"><span class="nv">$ </span>gem <span class="nb">install </span>rails</code></pre></figure>

You can even install just a specific version of the library, using the
`--version` / `-v` flag:

<figure class="highlight"><pre><code class="language-sh" data-lang="sh"><span class="nv">$ </span>gem <span class="nb">install </span>rails <span class="nt">--version</span> 5.0</code></pre></figure>

#### Listing all gems

For a **list** of all locally installed gems:

<figure class="highlight"><pre><code class="language-sh" data-lang="sh"><span class="nv">$ </span>gem list</code></pre></figure>

To obtain a (very long) list of all gems available on RubyGems.org:

<figure class="highlight"><pre><code class="language-sh" data-lang="sh"><span class="nv">$ </span>gem list <span class="nt">-r</span></code></pre></figure>

#### Help!

Documentation is available inside your terminal:

<figure class="highlight"><pre><code class="language-sh" data-lang="sh"><span class="nv">$ </span>gem <span class="nb">help</span></code></pre></figure>

For instance, `gem help commands` is very useful as it outputs a list of
all `gem`’s commands.

#### Crafting your own gems

RubyGems.org has [several guides][3] about this topic. You may also want
to investigate [Bundler][9], a generic tool which helps you manage an
application’s dependencies and may be used along RubyGems.



[1]: https://rubygems.org/
[2]: https://rubygems.org/pages/download/
[3]: http://guides.rubygems.org/
[5]: https://github.com/
[6]: https://www.ruby-toolbox.com/
[7]: http://guides.rubygems.org/command-reference/
[9]: http://bundler.io/