Rob Scripts

Replace IPs in stdin with their DNS names

This script takes standard input and replaces any occurance of an IP address with its name as per a DNS lookup.

#!/bin/bash
#
# Rob Hutten, 2015
# http://hutten.org/rob/scripts
# Reads from stdin; replaces IP addresses with their names
# as found in the DNS.

PATH=/bin:/usr/bin
sedscript=$(mktemp /tmp/poot.XXXXX)
input=$(mktemp /tmp/toot.XXXXX)

cat > $input

ips=($(tr ' ,:' '\012\012\012' < $input \
	| egrep '^[0-9\.][0-9\.]*$' \
	| egrep '[0-9]' \
	| egrep '\.' \
	| sort | uniq))

cat > $sedscript << EOF
#!/usr/bin/sed -f
EOF

for ip in ${ips[@]} ; do
        dns=$(host $ip | rev | awk '{print $1}' | rev | cut -d\. -f1)
        if [[ $dns =~ SERVFAIL ]] ; then
                dns=$ip
        fi
        echo s/${ip}/${dns}/g >> $sedscript
done

chmod +x $sedscript

$sedscript < $input
rm -f $sedscript $input

Tags: bash, dns, IP