$ sudo apt-get update
$ sudo apt-get install ruby-em-http-request 

ruby-em-http-request is installed in your system.

Make ensure the ruby-em-http-request package were installed using the commands given below,

$ sudo dpkg-query -l | grep ruby-em-http-request *

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

ruby-em-http-request package basic information: