Zabbix-sender on bash

zabbix_sender.sh

#!/bin/ash
help="Usage: zabbix_sender.sh <-z zabbix server> [-p server port] [-s host name] <-k key name> <-o key value>"
while getopts "z:p:s:k:o:h" c; do
        case $c in
                z)z=${OPTARG};;
                p)p=${OPTARG};;
                s)s=${OPTARG};;
                k)k=${OPTARG};;
                o)o=${OPTARG};;
                h)echo $help;exit 0;;
        esac
done

data='{"request":"sender data","data":[{"host":"'${s:-$HOSTNAME}'","key":"'${k:?$help}'","value":"'${o:?$help}'"}]}'
for i in `seq 0 7` ; do
	#Works in busybox. GNU printf needs the format string to be '\\x%x' instead.
        length="$length$(printf '\x%x' $(((${#data}/256**$i)%256)))"
done

resp=$(echo -n -e 'ZBXD\x01'$length$data | nc ${z:?$help} ${p:-10051})
if [ -z "${resp##*failed\:\ 1*}" ] ; then
        >&2 echo "Err: sending failed"
        exit 1
fi