Install Gem from Github Branch?

To update @Archonic answer, you need to replace the git protocol per the https protocol

fatal: remote error:
  The unauthenticated git protocol on port 9418 is no longer supported.

Therefore, you need to write:

gem 'rails', git: 'https://github.com/rails/rails.git', ref: '4aded'
gem 'rails', git: 'https://github.com/rails/rails.git', branch: '2-3-stable'
gem 'rails', git: 'https://github.com/rails/rails.git', tag: 'v2.3.5'

I have to modify @janic_'s answer to make it work. Hope it will help other ruby noobs like myself.

1. Clone the Git repository.

   $ git clone git://github.com/odorcicd/authlogic.git
   

2. Change to the new directory.

   $ cd authlogic
   

3. Checkout branch

   $ git checkout -b rails3 remotes/origin/rails3
   

4. Install bundles

   $ bundle install
   

5. Build the gem.

   $ rake build
   

6. Install the gem.

   $ gem install pkg/gemname-1.23.gem
   

1. Clone the Git repository.

   $ git clone git://github.com/odorcicd/authlogic.git
   

2. Change to the new directory.

   cd authlogic
   

3. Checkout branch

   $ git checkout -b rails3 remotes/origin/rails3
   

4. Build the gem.

   $ rake build gem
   

5. Install the gem.

   $ gem install pkg/gemname-1.23.gem
   

You don't need to build the gem locally. In your gemfile you can specify a github source with a ref, branch or tag.

gem 'rails', git: 'git://github.com/rails/rails.git', ref: '4aded'
gem 'rails', git: 'git://github.com/rails/rails.git', branch: '2-3-stable'
gem 'rails', git: 'git://github.com/rails/rails.git', tag: 'v2.3.5'

Then you run bundle install or the short form is just bundle.

Read more about it here: http://bundler.io/man/gemfile.5.html#GIT

Update: There's a github source identifier.

gem 'country_select', github: 'stefanpenner/country_select'

However, they warn against using it: NOTE: This shorthand should be avoided until Bundler 2.0, since it currently expands to an insecure git:// URL. This allows a man-in-the-middle attacker to compromise your system.

After Bundler 2.0, you can get around the above issue with this statement near the top of the Gemfile:

git_source(:github) { |repo| "https://github.com/#{repo}.git" }