script fragment: PTR=`dig @some.dns +short +norec -x a.b.c.d` echo "$PTR" if [ "$PTR" == "" ] ; then echo "$PTR" >> /path/to/PTR_absent.txt fi =========== output for an IP: a-b-c-d.domain.net. [: a-b-c-d.domain.net.: unexpected operator thanks Len