rotate string

rot.sh

#!/bin/bash -
#
# SCRIPT: rot
# AUTHOR: Luciano D. Cecere
#
########################################################################
#
# rot - rotate the alphabet and encode a string
# Copyright (C) 2014 Luciano D. Cecere <ldante86@aol.com>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
#########################################################################

PROGNAME="${0##*/}"

_rot()
{
while read input
do
  case $1 in
    0 )  echo "$input" ;; # no rotation
    1 )  tr 'A-Za-z' 'B-ZA-Ab-za-a' <<< "$input" ;;
    2 )  tr 'A-Za-z' 'C-ZA-Bc-za-b' <<< "$input" ;;
    3 )  tr 'A-Za-z' 'D-ZA-Cd-za-c' <<< "$input" ;;
    4 )  tr 'A-Za-z' 'E-ZA-De-za-d' <<< "$input" ;;
    5 )  tr 'A-Za-z' 'F-ZA-Ef-za-e' <<< "$input" ;;
    6 )  tr 'A-Za-z' 'G-ZA-Fg-za-f' <<< "$input" ;;
    7 )  tr 'A-Za-z' 'H-ZA-Gh-za-g' <<< "$input" ;;
    8 )  tr 'A-Za-z' 'I-ZA-Hi-za-h' <<< "$input" ;;
    9 )  tr 'A-Za-z' 'J-ZA-Ij-za-i' <<< "$input" ;;
    10)  tr 'A-Za-z' 'K-ZA-Jk-za-j' <<< "$input" ;;
    11)  tr 'A-Za-z' 'L-ZA-Kl-za-k' <<< "$input" ;;
    12)  tr 'A-Za-z' 'M-ZA-Lm-za-l' <<< "$input" ;;
    13)  tr 'A-Za-z' 'N-ZA-Mn-za-m' <<< "$input" ;; # rot13
    14)  tr 'A-Za-z' 'O-ZA-No-za-n' <<< "$input" ;;
    15)  tr 'A-Za-z' 'P-ZA-Op-za-o' <<< "$input" ;;
    16)  tr 'A-Za-z' 'Q-ZA-Pq-za-p' <<< "$input" ;;
    17)  tr 'A-Za-z' 'R-ZA-Qr-za-s' <<< "$input" ;;
    18)  tr 'A-Za-z' 'S-ZA-Rs-za-r' <<< "$input" ;;
    19)  tr 'A-Za-z' 'T-ZA-St-za-s' <<< "$input" ;;
    20)  tr 'A-Za-z' 'U-ZA-Tu-za-t' <<< "$input" ;;
    21)  tr 'A-Za-z' 'V-ZA-Uv-za-u' <<< "$input" ;;
    22)  tr 'A-Za-z' 'W-ZA-Vw-za-v' <<< "$input" ;;
    23)  tr 'A-Za-z' 'X-ZA-Wx-za-w' <<< "$input" ;;
    24)  tr 'A-Za-z' 'Y-ZA-Xy-za-x' <<< "$input" ;;
    25)  tr 'A-Za-z' 'Z-ZA-Yz-za-y' <<< "$input" ;;
    * )  _help ;;
  esac
done
}

_help()
{
    echo $PROGNAME - encode a string by rotation
    echo Usage: $PROGAME [0-25]
    echo Default rotation is 13 \(rot13\)
    exit 0
}

_rot ${1:-13}