ROT13 ("rotate by 13 places", sometimes hyphenated ROT-13) is a simple letter substitution cipher that replaces a letter with the 13th letter after it in the alphabet. ROT13 is a special case of the Caesar cipher which was developed in ancient Rome.
fire up your linux terminal and type the below command
alazar@alazar-Latitude-E4310:~ make
alazar@alazar-Latitude-E4310:~ sudo chmod +x rot13
alazar@alazar-Latitude-E4310:~ ./rot13 <message_to_either_encrypt_or_decrypt>