Required ruby installation

To install ruby 2.1.5 you can use either of methods(assuming Ubuntu)

1. Compile

Compile from source. sudo gem install is used to install ruby gems

Remove the old Ruby 1.8 if present

sudo apt-get remove ruby1.8

Download Ruby and compile it

mkdir /tmp/ruby && cd /tmp/ruby
curl -L --progress http://cache.ruby-lang.org/pub/ruby/2.1/ruby-2.1.5.tar.gz | tar xz
cd ruby-2.1.5./configure --disable-install-rdoc
make
sudo make install

Install the Bundler Gem

sudo gem install bundler --no-ri --no-rdoc

2. RVM

Use Ruby Version Mananger. gem install to install ruby gems

Install RVM author's public key

gpg --keyserver hkp://keys.gnupg.net --recv-keys D39DC0E3

Install RVM with ruby(sudo password might be asked)

curl -sSL https://get.rvm.io | bash -s stable --ruby=2.1.5

Activate RVM

source ~/.rvm/scripts/rvm