In order to install Sass on Ubuntu, you'll first need to install ruby 1.8.7+ and rubygems.

To install ruby, run the command below

$ sudo apt-get install ruby-full build-essential

Next, Install rubygems by running

$ sudo apt-get install rubygems

Once those are both installed, you'll be able to install Sass

$ sudo gem install sass

If you are installing rubygems for the first time, you may need to update your system PATH variable. To do that, you'll need to open your ./bashrc file

$ vi ./bashrc

and then add the following line

export PATH=$PATH:/var/lib/gems/1.8/bin  

Now, run the following command to verify that SASS has been installed

$ sass -v
Sass 3.2.12 (Media Mark)