Setup Ruby on Rails with ruby 2 and rails 4 into ubuntu 14.04

Ruby Installation:

sudo apt-get update

sudo apt-get install git-core curl zlib1g-dev build-essential libssl-dev libreadline-dev libyaml-dev libsqlite3-dev sqlite3 libxml2-dev libxslt1-dev libcurl4-openssl-dev python-software-properties

Then you can install via RVM with following few commands:

sudo apt-get install libgdbm-dev libncurses5-dev automake libtool bison libffi-dev
curl -L https://get.rvm.io | bash -s stable
source ~/.rvm/scripts/rvm
echo "source ~/.rvm/scripts/rvm" >> ~/.bashrc

Then reload your shell or open new terminal window for get changes.

Check that rvm is installed or not:

$ type rvm | head -1
output: rvm is a function

Install ruby 2.0.0 version:
rvm install 2.0.0

If you want to change version then change new version with 2.0.0

rvm use ruby-2.0.0-p481 --default

then check for ruby version:

ruby -v

Rails Installation:

Since Rails have so many dependencies these days, 
Here is a install of Javascript runtime like NodeJS. 

sudo add-apt-repository ppa:chris-lea/node.js
sudo apt-get update
sudo apt-get install nodejs
gem install rails

If you want to choose specific version then install via this command:

gem install rails -v 4.0.0