bash replace ip with hostname using nslookup on a file

Question

i have a tempfile that outputs this information

1.2.3.4 34
1.2.3.5 23
1.2.3.6 22

The first columns are ip adresses, and the second one are simultaneos connections to databases, i need to output the first column not as an ip address but as a hostame, and keep the info of the second column

Desired output

hostname1 34
hostname2 23
hostname3 22

thanks in advance...

Answer 1

Something like this maybe:

#!/bin/bash
while read ip n
do
   # Uncomment following to use /etc/hosts
   # name=$(awk -v ip=$ip '$1 ~ ip{print $2}' /etc/hosts)
   # Uncomment following to use nslookup
   # name=$(nslookup $ip| grep "name ="|sed 's/.*=//')
   # Uncomment following line to use dig (thanks to Charles Duffy)
   # name=$(dig +short -x $ip)
   echo $name $n
done < file

Answer 2

Not entirely sure what you want to achieve, but this will literally get the "desired output"

awk 'BEGIN {x = 1} {printf "hostname%s %s\n", x, $2; x += 1}' tempfile

Answer 3

How about logresolve from apache2-utils? It detects what looks like an IP address and replaces it with the resolved hostname:

$ cat tempfile
1.2.3.4 34
1.2.3.5 23
1.2.3.6 22

$ cat tempfile | logresolve
hostname1 34
hostname2 23
hostname3 22