shell> perldoc -q 'ip address'
Found in /usr/lib/perl5/5.6.1/pod/perlfaq9.pod

How do I find out my hostname/domainname/IP address?

The normal way to find your own hostname is to call the "`hostname`" program. While sometimes expedient, this has some problems, such as not knowing whether you've got the canonical name or not. It's one of those tradeoffs of convenience versus portability.

The Sys::Hostname module (part of the standard perl dis- tribution) will give you the hostname after which you can find out the IP address (assuming you have working DNS) with a gethostbyname() call.

     
    use Socket;
    use Sys::Hostname;
    my $host = hostname();
    my $addr = inet_ntoa(scalar gethostbyname($host || 'localhost'));
[download]

Probably the simplest way to learn your DNS domain name is to grok it out of /etc/resolv.conf, at least under Unix. Of course, this assumes several things about your resolv.conf configuration, including that it exists.

(We still need a good DNS domain name-learning method for non-Unix systems.)