Simple script to loop through a list of IP addresses and output their resolutions

fast_resolver.sh

#!/bin/sh
cat ips.txt | while read ip
do
  echo $ip " " & host $ip | cut -f 5 -d " "
done

ips.txt

# just add 1 IP per line
192.168.1.1
192.168.1.2
192.168.1.3
192.168.1.4
192.168.1.5

ok, i was playing around with this a little more. and it really depends on the output of the commands on how easy this can be. i think this new version may work best.

awk -F " " '{print $1}' file.txt |sort -u | xargs -I % sh -c 'printf "% "; dig +short -x % |xargs |grep . && continue || echo "NXDOMAIN"'

Breakdown:

1. for the first awk, same info as i had above. if the IP is in a known location, this should be easy to set. if the file is only IP addresses, then you wouldn't need the -F and you can print $0.
2. the sort -u obviously sorts in order and only pulls out the unique IPs
3. then you pipe it to "xargs", which makes it easier to pipe into a few system commands (maybe there's an easier way).
4. i used printf so that it would just print the IP address and not a newline character (for some reason, i couldn't get "echo -n" to work
5. i then settled on "dig +short" so that the response was consistent, and easier to read. the downside is that if there is no result, it doesn't return anything (hence the upcoming grep statement)
6. the 2nd xargs is really there for when dig responds with multiple domains tied to the IP in question - it will keep all results on the same line, space delimited, vs. a newline
7. finally, i wanted to easily know when dig did not find a result. so i piped the output to grep and just searched for a dot. if there was a response from dig, it'll be found and the script will continue. if it is not found, it'll print out NXDOMAIN, and then continue on

all in all, it's still a nice one-liner so you don't have to have a script file to run and it's pretty fast. output looks roughly like this:

10.11.12.13 NXDOMAIN
10.22.33.44 10-22-33-44.somedomain.net
10.44.22.55 10-44-22-55.someotherdomain.net specialsystem.domain.net

thanks!