Extract IP address from a string

Question

The Linux host command returns:

hostA.domain.com has address xx.xxx.xxx.xx

How do I get just the IP address and put it in the $ipaddr variable?

open(FILE, "hostlist.txt") or die("Unable to open file");
@hostnames = <FILE>;
close(FILE);
foreach $hostname (@hostnames)
{
    $lookup = qx(host $hostname);
    $ipaddr = grep ip_address $lookup;  <---- need help here
    print $ipaddr;
}

Answer 1

Since you posted this on the Unix & Linux site, instead of StackOverflow, I'm wondering if something like this isn't what you're looking for:

cat hostlist.txt | xargs resolveip -s

This will only return one IP address though.

Some hostnames will have multiple IP addresses associated with them:

$ host www.google.com
www.google.com is an alias for www.l.google.com.
www.l.google.com has address 74.125.227.18
www.l.google.com has address 74.125.227.17
www.l.google.com has address 74.125.227.16
www.l.google.com has address 74.125.227.20
www.l.google.com has address 74.125.227.19

To get just the list of IPs, one way to do it is:

host <hostname> | grep "has address" | awk '{print $4}'

If you want to stick with Perl, using resolveip:

$ipaddr = qx(resolveip -s $hostname);

Or to get all of the IPs, without executing any shell commands:

use Socket;
@ipaddrs = map { inet_ntoa($_) } (gethostbyname($hostname))[4,];

Answer 2

Why not just use dig +short?

Answer 3

I'd use something like:

(\d{1,3}\.){3}\d{1,3}

If you want something more exacting, then you'll probably have:

([012]?\d{1,2}\.){3}[012]?\d{1,2}

But even this is still somewhat loose. For example, it still allows '269.278.287.296' to falsely match.

But both match the standard 0.0.0.0 to 255.255.255.255.

Answer 4

To add to @mkopala 's answer, if you have multiple hosts and you want to keep a track of them, build a hash, so that there is a easy reference of host to ip mapping.

Example:

#!/usr/bin/perl
use Socket;
@hostnames = ('www.google.com', 'www.yahoo.com', 'www.facebook.com');
%ipaddrs = ();
foreach $hostname (@hostnames) {
        map { $ipaddrs{$hostname} = inet_ntoa($_) } (gethostbyname($hostname))[4,];
}