#!/bin/sh
# $Id: rot13,v 1.2 2000/02/10 22:30:56 friedman Exp $

from='[a-m][n-z][A-M][N-Z]'
  to='[n-z][a-m][N-Z][A-M]'

case $# in
  0 ) exec             tr "$from" "$to" ;;
  * ) echo ${1+"$@"} | tr "$from" "$to" ;;
esac