Failed generating controller due to Bundler version conflict - ruby-on-rails

Question

I'm learning Rails with tutorials from Ruby on Rails by Michael Hartl: https://www.railstutorial.org/book
I used the following command to generate a controller:
rails generate controller StaticPages home help
Which generates the following error regarding version conflicts:
check_version_conflict': can't activate bundler-1.12.4, already
activated bundler-1.13.0.pre.1 (Gem::LoadError)
I don't know which bundler version to use. The current version of bundler is: 1.13.pre.1
The following command continued failing due to about five gem dependencies that failed to install automatically, which included listen and nokigiri.
bundle install --without production
I tried installing the dependent gems manually, but I'm still having issues.
How do I resolve the check_version_conflict issue with Bundler when generating Rails controllers?
I'll accept an answer that instructs removing current Ruby libs and installing a new development environment from scratch.

Answer 1

Bundler will install project-specific versions of your gems so that you don't have to manage global dependencies.
In effect, if you install Rails with bundler and you also install it with sudo gem install rails or something like that, you'll have two versions on your computer. By default, calling rails will refer to the global version.
If you call bundle exec rails (or bundle exec <gem_name>), it will call the bundler-specific version.

Answer 2

Ten steps to resolve your issues with Bundler
(optional) Uninstall Ruby. There are many ways to do so, here's one: https://superuser.com/questions/194051/how-to-completely-remove-ruby-ruby-gems-on-mac-os-x-10-6-4
(optional) Use rbenv to install Ruby. Follow instructions here: https://github.com/rbenv/rbenv
Make a repo directory that will house your future Rails app
From the command line:
mkdir repo
cd repo
Install Bundler and create a Gemfile for the directory
From the command line:
gem install bundler
bundle init
Open the repo/Gemfile with your editor, and configure it to instruct Bundler which version of Rails to install
In repo/Gemfile:
source "https://rubygems.org"
gem "rails", "4.2.6"
Install Rails via Bundler
From the command line:
bundle install
Create a new Rails app using Bundler, and cd into it
From the command line:
bundle exec rails new whatevs
cd whatevs
Your Rails app will have a Gemfile by default. Open it and add the gems you wish to use in your app.
In repo/whatevs/Gemfile:
gem 'nokogiri', '1.6.8'
From repo/whatevs/ directory, install your app's Gems via Bundler
From the command line:
bundle install
From repo/whatevs/ directory, generate a controller
From the command line:
bundle exec rails generate controller static_pages home help