#!/bin/sh

usage () {
    echo "usage $0 [-i] EXT1 EXT2 [DIR]" > /dev/stderr
    exit 1
}

confirm () {
    echo -n "rename $1? "
    read ANSWER
    case $ANSWER in
        y*|Y*) mv $1 $(basename $1 .$2).$3;;
    esac
}
    
CONFIRM=

if [ $# -lt 2 -o $# -gt 4 ]
then
    usage
fi

case $1 in
    -i) CONFIRM="present"; shift;
        if [ $# -lt 2 ]
        then
            usage
        fi;;
    -*) usage;;
     *) if [ $# -eq 4 ]
        then
            usage
        fi;;
esac

EXT1=$1; shift; EXT2=$1; shift;
if [ $# -gt 0 ]
then
    DIR=$1; shift
else
    DIR='.'
fi

if [ -n $CONFIRM ]
then
    for i in $(/bin/ls $DIR/*.$EXT1 2> /dev/null)
    do
        confirm $i $EXT1 $EXT2
    done
else
    for i in $(/bin/ls $DIR/*.$EXT1 2> /dev/null)
    do
        mv $i `basename $i .$EXT1`.$EXT2;
    done
fi
exit 0