I have just started learning Ruby for personal interest following the Hackerrank section available for practice. If you want you can visit the page here and start solving challenges.
This small article describes one of the challenges I have solved about a ROT13 cypher decoder. Basically, ROT13 is a simple letter substitution cipher that replaces a letter with the 13th letter after it, in the alphabet. [more info]
Follows my solution to the challenge on Hackerrank Ruby practice.