#!/bin/sh
#####################
#
# name: rot (rot.sh)
# vers: 0.1a
# date: 031506
# auth: "Keith Beckman" <kbeckm@alphahelical.com>
# site: http://alphahelical.com/code/scripts/rot
# desc: rot applies substitution cyphers to text in a case-sensitive.
# manner. It is essentially a front-end for tr(1), with its main
# features being that it allows input either from the command line
# or from stdin, that it keeps a set of predefined substitutions,
# and that it simplifies substitution with a user-definable
# default behaviour.
#
#####################

####configuration####

default_mode='anrot'
verstring='rot v0.1a 031506 Keith Beckman'

##end configuration##

# Define our various alphabets for use in translation, so we can define
# various rot13/atbash implementations (really, any simple substitution cypher)

alpha='abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
alpharot='nopqrstuvwxyzabcdefghijklmNOPQRSTUVWXYZABCDEFGHIJKLM'

alphanum='abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'
alphanumrot='nopqrstuvwxyzabcdefghijklmNOPQRSTUVWXYZABCDEFGHIJKLM5678901234'
atbash='zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA9876543210'

rot_usage () {
 echo 'Usage: rot -[a|n|b|h|v] [input text]'
 echo ' rot applies substitution cyphers to stdin.'
 echo ' Default behaviour is alphanumeric rot13.'
 echo ' a: alpha-only rot13'
 echo ' b: atbash (reversed alphabet)'
 echo ' n: alphanumeric rot13'
 }

# Check args to allow no flags but still input text.
if [ $2 ]; then
 modearg=$1
 inputarg=$2
elif [ $(echo $1 | grep "^-") ]; then
 modearg=$1
 inputarg=$2
else
 modearg=''
 inputarg=$1
fi

# Choose mode, and default to alphanumeric-a
case $modearg in

# modes
 '-a') #alpha-only rot13
  mode='arot'
  ;;
 '-b') #atbash
  mode='atbash'
  ;;
 '-n') #alphanumeric rot13
  mode='anrot'
  ;;

# other options
 '') #default mode
  mode=$default_mode
  ;;
 '-v') #version
  echo $verstring
  echo ' Apply substitution cyphers to stdin.'
  exit
  ;;
 '-h') #help
  rot_usage
  exit
  ;;
 *) #bad option
  echo 'Please specify a valid option.'
  rot_usage
  exit
  ;;
 esac

# Set up substitutions based on mode
case $mode in
 'arot') #alpha-only rot13
  first=$alpha
  second=$alpharot
  ;;
 'anrot') #alphanumeric rot13
  first=$alphanum
  second=$alphanumrot
  ;;
 'atbash') #atbash
  first=$alphanum
  second=$atbash
  ;;
 esac

# Make allowance for command-line text input
if [ $inputarg ]; then
 echo $inputarg |
 tr $first $second 2> /dev/null
else
 tr $first $second 2> /dev/null
fi

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