RubyGems ships with Ruby 1.9+. There is nothing to install. For prior versions of Ruby, see package instructions to install RubyGems.
Upgrade
To upgrade RubyGems.
gem update --system
Documentation
All gems have documentation that is generated when installing a gem. To start the documentation web server.
gem server
To view the documentation, point your web browser to http://localhost:8808/.
Automatically Starting the Documentation Server at Boot
Create a configuration file for Launchd.
sudo nano /Library/LaunchDaemons/org.rubygems.gem.plist
Copy and paste the following text into the aforementioned file. The path to the gem executable cannot use the rbenv shim binary because the environment in your startup script never gets set up. Pick your primary version of Ruby and use an absolute path to the gem executable. Make sure you update the path in the configuration below.
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Label</key>
<string>org.rubygems.gem</string>
<key>ProgramArguments</key>
<array>
<string>/usr/local/rbenv/versions/1.9.3-p125/bin/gem</string>
<string>server</string>
<string>--daemon</string>
</array>
<key>RunAtLoad</key>
<true/>
<key>KeepAlive</key>
<true/>
</dict>
</plist>
And finally, execute the following command to register the configuration file with Launchd.
sudo launchctl load -w /Library/LaunchDaemons/org.rubygems.gem.plist
If you ever want to stop your documentation server from automatically starting at boot, issue the following command.
sudo launchctl unload -w /Library/LaunchDaemons/org.rubygems.gem.plist