Setup dev env on Mac Sierra

Development env Rails

Open terminal
> ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
Say yes to X-Code (have fast connection for download)
> brew install rbenv ruby-build

Add rbenv to bash so that it loads every time you open a terminal
> echo 'if which rbenv > /dev/null; then eval "$(rbenv init -)"; fi' >> ~/.bash_profile
> source ~/.bash_profile

 Install Ruby
> rbenv install 2.4.0
> rbenv global 2.4.0
> ruby -v

More on rbenv

rbenv-bundler is a near-invaluable plugin that makes the rbenv shims Bundler-aware and alleviates you from needing to type 
bundler exec in front of every command. It is also easy to install straight from Github.

git clone git://github.com/carsomyr/rbenv-bundler.git ~/.rbenv/plugins/bundler
Bundler is the only Gem that you need install the traditional way. You will need to do this once for each version of Ruby 
that you have. The rehash command updates the shim for the bundle binary.

gem install bundler
rbenv rehash

To start a new project
To find out what the most recent Rails version is, use the command  gem search rails | grep "^rails ". 

Create a directory for your application along with a Gemfile to specify your desired Rails version and 
let Bundler install the dependent gems:

cd /tmp/rails-apps
mkdir my-first-app
cd my-first-app
echo "source 'https://rubygems.org'" > Gemfile
echo "gem 'rails', '5.0.1'" >> Gemfile
bundle install
Check that the correct version has been installed using bundle exec rails -v or if you installed the plugin above just rails -v

Now create your application, let Rails create a new Gemfile (or rather overwrite the existing one by using the --force flag) and
instead of installing the bundle (--skip-bundle) update it manually:

bundle exec rails new . --force --skip-bundle 
or just if plugin installed
rails new myapp -d postgresql
rails new . -d postgresql --force --skip-bundle
bundle update