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

libmapscript-ruby is installed in your system.

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

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

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

libmapscript-ruby package basic information: