sh variable not working if blank - bash

Question

Need some extra eyes for this one...
dns_lookup() {
ip_set
if [ `ip_ping ${ip_address}` -eq 0 ]
then
host=""
dig +short -x ${ip_address} | sed 's/\.$//g' | while read host
do
if [ -z "${host}" ]
then
host="unknown"
fi
echo "${ip_address},${host}"
done
fi
}
I get desired results if ip is pingable and has a dns name. I do not get results if the ip is pingable but does not have a dns name.
ip_set() {
ip_address="${a}.${b}.${c}.${d}"
}
ip_ping() {
timeout ${delay} ping -q -c 1 -i 1 -W 1 -w 4 $1 > /dev/null 2>&1 ; echo $?
}

Answer 1

Perhaps this is what you need. Tell me if you need revisions.
dns_lookup() {
ip_set
if [ `ip_ping ${ip_address}` -eq 0 ]
then
host=""
dig +short -x ${ip_address} | sed 's/\.$//g' | {
hashosts=false
while read host
do
if [ -n "${host}" ]
then
hashosts=true
echo "${ip_address},${host}"
fi
done
[ "${hashosts}" = false ] && echo "${ip_address},unknown"
}
fi
}
I would have also suggested the change of function ip_ping but that_other_guy already did it.

Answer 2

You don't get a result when there's no hostname because your while read loop never runs when there are no lines to read. You should make your printing code run regardless:
host=$(dig +short -x "${ip_address}" | sed 's/\.$//g')
if [ -z "${host}" ]
then
host="unknown"
fi
printf "${ip_address},%s\n" $host
Also, you're going about your condition wrong. You shouldn't echo the exit status and compare it as text. You should just let your command's exit status be your function's exit status:
ip_ping() {
timeout ${delay} ping -q -c 1 -i 1 -W 1 -w 4 $1 > /dev/null 2>&1
# functions implicitly 'return $?' if you don't specify anything else
}
Now you can easily check your function:
if ip_ping "$ip_address"
then
echo "It worked"
else
echo "It failed.."
fi