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

libtcltk-ruby is installed in your system.

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

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

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

libtcltk-ruby package basic information: