check the dns record for a hostname with nslookup - linux

Question

I have a host list hostfile that i'm doing name lookup just to know if the host has records in DNS or not with the help of Linux native tool nslookup.
Below is what i'm doing and its working, however there is a situation when nslookup don't find anything thus the result is nothing in that case i want to fill "no dns record"
What i'm trying:
$ for i in `cat hostfile`;
> do
> echo $i $result
> result=$(nslookup $i | awk 'FNR==6{print $2}')
> done
OR
for i in `cat hostfile`;
do
printf "$i: %s\\n" $(nslookup $i | awk 'FNR==6{print $2}');
done
Its not giving correct output if there is no nslookup found.
Desired:
myhosts01 192.168.1.1
myhosts02 192.168.1.2
myhosts03 192.168.1.3
myhosts04 192.168.1.4
myhosts03 no dns record
myhosts04 no dns record

Answer 1

You can either use a full if statement to check whether the result is blank (-z for zero-length):
if [[ -z "$result" ]]; then
result="no dns record"
fi
echo "$i $result"
Or use a default value when expanding the variable:
echo "$i ${result:-no dns record}"
In either case, I'd recommend using a while read loop to read the file instead of for (assuming there's one hostname per line), using dig +short instead trying to parse nslookup, doing the lookup before printing the result, and double-quoting all variable references (and probably using more descriptive variable names). Something like this:
while read -r hostname; do
hostIP=$(dig +short "$hostname")
echo "$hostname ${hostIP:-no dns record}"
done <hostfile