Many different ways to resolve an IP to a hostname in Perl

Some different ways to look up hostnames.

Notes:

• getnameinfo() gets a hostname and a service name, so it's not exactly the same as gethostbyaddr()
• although the docs imply you need to enter a port, that's just to get the local service name. If you set it as undef then you can ignore any service

# 1, old deprecated way

use Socket; # gethostbyaddr, inet_aton, AF_INET

sub ip_address_to_host {

    my ( $self, $ip_address ) = @_;

    my ($hostname) = gethostbyaddr(

        inet_aton($ip_address),

        AF_INET,

    );

    return $hostname;

}

# 2, newer better way

use Socket qw(AF_INET inet_pton getnameinfo sockaddr_in);

sub ip_address_to_host {

     my ( $self, $ip_address ) = @_;

    my $port = undef;

    my $socket_address = sockaddr_in($port, inet_pton(AF_INET, $ip_address));

    my $flags = 0;

    my $xflags = 0;

    my ($error, $hostname, $servicename) = getnameinfo($socket_address, $flags, $xflags);

    return $hostname;

}

# 3, best way - that only uses DNS and not /etc/hosts first

use Net::DNS;

sub ip_address_to_host {

     my ( $self, $ip_address ) = @_;

    my $res = Net::DNS::Resolver->new;

    my $target_ip = join('.', reverse split(/\./, $ip_address)).".in-addr.arpa";

    my $query = $res->query("$target_ip", "PTR") // return;

    my $answer = ($query->answer)[0] // return;

    my $hostname = $answer->rdatastr;

    return $hostname;

}

# 4, the code golf way (no validation) - by Mark B

 perl -le 'use Net::DNS::Resolver; print ((Net::DNS::Resolver->new()->query("10.232.32.158","PTR")->answer)[0]->ptrdname);'

(source, source, source)