Ruby Bundler

From Gem Versioning and Bundler: Doing it Right

Key pointers from the article

• When running an executable, ALWAYS use bundle exec [command]. Quoting from the bundler documentation: In some cases, running executables without bundle exec may work, if the executable happens to be installed in your system and does not pull in any gems that conflict with your bundle. However, this is unreliable and is the source of considerable pain. Even if it looks like it works, it may not work in the future or on another machine.
• When you run an executable from the command line without bundle exec, this wrapper invokes Rubygems, which then uses the normal Rubygems activation mechanism to invoke the gem’s executable. This has changed in the past several months, but Rubygems will invoke the latest version of the gem installed in your system, even if your Gemfile.lock specifies a different version. In addition, it will activate the latest (compatible) installed version of dependencies of that gem, even if a different version is specified in your Gemfile.lock.
• The only exception to the above rules is the rails executable. As of Rails 3.0, the executable simply looks for a script/rails file, and execs that file. The generated script/rails loads the local boot environment, which invokes bundler immediately.

This explains when the Gemfile specifies Rails gem of "3.0.5", and the system Rails gem is "3.1.0", typing the command "rails -v" inside and outside the application root directory gives different version value

Inside application root directory:

06:12 PM ~/Development/rails_projects/app_0515 $ rails -v

rails Rails 3.0.5

Outside application root directory:

06:21 PM ~/Development/rails_projects $ rails -v

Rails 3.1.0