My Password Generator v2.0

#!/bin/sh

LOG="$HOME/.my_password_generator.log"

echo -n "Enter [Key]: "
stty -echo
read key
stty echo
# echo "[$key]"         # -- for debug only -- #
echo "*******************"
echo -n "Enter [Start Len]: "
read start len

[ -z "$start" ] && echo "Pleas enter 'Start'" && exit
[ -z "$len" ] && echo "Pleas enter 'Len'" && exit

L=$key
K=""
end=`expr $start + $len - 1`
for i in `seq 1 129`; do
        L=`echo -n $L | sha512sum -b | cut -f1 -d' '`
        K="$K$L"
done
B=`echo $K | xz -c -f | base64 -w0`
echo -n $B | cut -c${start}-${end}
FP=`echo -n $B | sha512sum | cut -c1-4,125-128 | tr 'a-f' 'A-F'`
echo "fingerprint: $FP"
[ -e "$LOG" ] && echo "`date` | $FP $start" >> $LOG