brew gem allows you to install any rubygem as a homebrew formula.

It works by generating a stub formula for homebrew, which looks something like this:

class Ronn < Formula
  def initialize(*args)
    @name = "ronn"
    @version = "0.7.3"
    super
  end

  def install
    system "gem", "install", name, "--version", version, "--install-dir", prefix
  end
end

This formula installs and unpacks all the dependencies under the Cellar path. So the package is completely self contained.

This requires a system rubygems version of 2.3 or greater There is a bug prior to 2.3 that doesn't install the full dependency tree properly when you use the install-dir flag.

sudo /usr/bin/gem update --system

There are two ways to install brew-gem, via Homebrew or via Rubygems. Usually the Rubygems release will track ahead of the Homebrew recipe, so to receive the latest features, use the Rubygems install instructions.

Warning: If you previously installed brew-gem with Homebrew, the Rubygems install method will fail. Run brew unlink brew-gem or brew uninstall brew-gem first.

Via Rubygems:

gem install brew-gem
brew-gem install brew-gem

Via Homebrew:

brew install brew-gem

brew gem install heroku

To install a specific version:

brew gem install heroku 3.8.3

To install using a brew installed ruby(/usr/local/bin/ruby):

brew gem install heroku --homebrew-ruby

And with a specific version:

brew gem install heroku 3.8.3 --homebrew-ruby

To upgrade:

brew gem upgrade heroku

To uninstall:

brew gem uninstall heroku

To check information:

brew gem info heroku

Note:

Installed gems are listed in brew list with prefix of gem-, like gem-heroku.

To make use of completions for your gem, you need to install the bash-completion formula:

brew install bash-completion

And then install a gem with the completion files in the following locations:

• A directory named either completion or completions with the file being the name of the gem appended with the completion type.

  For example: completions/tmuxinator.bash

• A file somewhere in your repo named <your_gem_name>_completion.zsh.

Files with .bash and .sh will be associated with bash and files ending in .zsh will be associated with zsh.

This is not for installing development libraries, but for standalone binary tools that you want system wide.

If your seeing build errors similar to this:

==> Fetching opsicle from gem source
==> gem install /Library/Caches/Homebrew/opsicle-0.4.2.gem --no-rdoc --no-ri --no-user-install --install-dir /usr/local/Cellar/opsicle/0.4.2 --bindir /usr/local/Cellar/opsicle/0.4.2/bin
make: *** [generator.bundle] Error 1
Gem files will remain installed in /usr/local/Cellar/opsicle/0.4.2/gems/json-1.8.1 for inspection.
Results logged to /usr/local/Cellar/opsicle/0.4.2/gems/json-1.8.1/ext/json/ext/generator/gem_make.out
READ THIS: https://github.com/Homebrew/homebrew/wiki/troubleshooting

You probably have xcode 5.1 installed which changed the way the compilers handle flags.

You'll need to set ARCHFLAGS=-Wno-error=unused-command-line-argument-hard-error-in-future before installing. You may want to add this to your profile so you don't have to set it each time.