Reads ip addresses from the command line or stdin and prints them if they belong to any of the three RFC1918 private address blocks

private-ip.pl

#!/usr/bin/perl -w

use Net::CIDR;
use Getopt::Long;

# Net::CIDR one liner:
#   perl -mNet::CIDR -ne 'print if Net::CIDR::cidrlookup($_, ("10.0.0.0/8", "172.16.0.0/12", "192.168.0.0/16"))'
#
# TODO: add ip address validation

sub usage {
	my $name = $0;
	$name =~ s/.*\///;
	print <<EOT;
Usage: $name [options] ip1 [ip2 ip3 ...]
Print ip addresses that belong to RFC1918 private address blocks.
Read ip numbers on the command line or from standard in.
Options:
	-h, --help:	print this message
	-n, --not:	print non-private ip addresses
EOT
}

sub filter_ip {
	my ($ip) = @_;
	print $ip, "\n" if Net::CIDR::cidrlookup($ip, @rfc1918_blocks) ^ $not;
}

BEGIN {
	my $help;
	our $not = 0;
	our @rfc1918_blocks = ('10.0.0.0/8', '172.16.0.0/12', '192.168.0.0/16');

	GetOptions(
		'help' => \$help,
		'h' => \$help,
		'not!' => \$not,
	);
	defined $help and usage() and exit;
}

if ($#ARGV > -1) {
	while ($#ARGV > -1) { # process every ip address on the command line
		filter_ip($ARGV[0]);
		shift;
	}
} else {
	while (<>) { # read from standard in if there's nothing on the command line
		chomp;
		filter_ip($_);
	}
}