rbenv

pi

$ cd /opt/src
$ git clone https://github.com/rbenv/rbenv.git
$ sudoedit /etc/profile.d/rbenv.sh

/etc/profile.d/rbenv.sh

export RBENV_ROOT=/opt/src/rbenv
export PATH="$RBENV_ROOT/bin:$PATH"
eval "$(rbenv init -)"

pi

$ source /etc/profile.d/rbenv.sh

ruby-build

pi

$ mkdir /opt/src/rbenv/plugins
$ cd /opt/src/rbenv/plugins
$ git clone git://github.com/sstephenson/ruby-build.git
$ cd /opt/src/rbenv/plugins/ruby-build
$ sudo ./install.sh

rbenv-gemset

pi

$ cd /opt/src/rbenv/plugins
$ git clone git://github.com/jamis/rbenv-gemset.git

rbenv-binstubs

pi

$ cd /opt/src/rbenv/plugins
$ git clone https://github.com/ianheggie/rbenv-binstubs.git

Ruby

pi

$ sudo apt-get install -y libreadline-dev
$ rbenv install 2.4.0
$ rbenv rehash
$ rbenv global 2.4.0