use strict;
use warnings;

local $/ = 'lease';
my $leaseFile = '/var/lib/dhcp3/dhcpd.leases';

open my $fh, '<', $leaseFile or die $!;

while (<$fh>) {
	my ($ip) = /\s+(\S+)\s+/ or next;
	my $client = /client-hostname\s+(".+")/ ? $1 : '';
	print "$ip,$client\n";
}

close $fh;