$ sudo apt-get update
$ sudo apt-get install libsphinx-ruby 

libsphinx-ruby is installed in your system.

Make ensure the libsphinx-ruby package were installed using the commands given below,

$ sudo dpkg-query -l | grep libsphinx-ruby *

You will get with libsphinx-ruby package name, version, architecture and description in a table

libsphinx-ruby package basic information: