ROT13

ROT13.sh

#https://en.wikipedia.org/wiki/ROT13

echo "Hail, Caesar!" | tr 'a-zA-Z' 'n-za-mN-ZA-M'
#Unvy, Pnrfne!

echo "Unvy, Pnrfne!" | tr 'a-zA-Z' 'n-za-mN-ZA-M'
#Hail, Caesar!

#To better understand this:
#tr accepts
#   set of characters to convert from
#   corresponding set of characters to convert to

echo "abc" | tr 'a-zA-Z' 'n-za-m N-ZA-M'
#nop
echo "mno" | tr 'a-zA-Z' 'n-za-m N-ZA-M'
#zab
echo "lowercase letters" | tr 'a-z' 'A-Z'
#LOWERCASE LETTERS