#!/bin/sh
# Copyright (C) 2003 Adalbert Prokop, adalbert.prokop(%)web.de

# 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 2 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, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

ROT13="$(basename "$0")"

function showhelp() {
cat <<+++
NAME
    $ROT13 - codes a textline, file or standard input by shifting
            all letters 13 positions to the right.
SYNOPSIS
    $ROT13 [-i inputfile] [-o outputfile] [-h] [text]

DESCRIPTION
    inputfile:  file to encode in rot13.

    outputfile: file, where the output will be written to

    -h: gives this help

    text: if no inputfile is specified, _text_ will be coded with
          rot13. If not given, the STD_IN will be coded

    If the outputfile is not specified, the STD_OUT will be use
+++
}

INPUTFILE=
OUTPUTFILE=
ABC=abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
CBA=nopqrstuvwxyzabcdefghijklmNOPQRSTUVWXYZABCDEFGHIJKLM

# eval: to get rid of those damned single quotes
eval set -- $(getopt -o hi:o: -n "$ROT13" -l help -- "$@")

while [ "$1" != "--" ]; do
    case "$1" in
        -h|--help) showhelp;
                   exit 0;;
        -i) INPUTFILE=$2; shift 2;;

        -o) OUTPUTFILE=$2; shift 2;;
    esac
done

shift # kill "--"

if [ "$INPUTFILE" ]; then
    INPUT="cat $INPUTFILE"
elif [ "$*" ]; then
    INPUT="echo \"$*\""
else
    INPUT="cat"
fi

if [ "$OUTPUTFILE" ]; then
    OUTPUT=">$OUTPUTFILE"
else
    OUTPUT=
fi

eval $INPUT| eval tr "$ABC" "$CBA" $OUTPUT