Perl script to parse ISC DHCP lease file and display basic info. I dont recall if I wrote this or if I found it on the interwebs somewhere!?!?.. a quick goog search did not find it but hey its useful so have at it.

leasecheck.pl

#!/usr/bin/perl
#
# Update the path to your lease file below
use strict;
use File::Copy;
#use DateTime;

#always parse a copy not the live file
#my $leasefile = '/var/lib/dhcpd/dhcpd.leases';
my $leasefile = '/var/lib/dhcp/db/dhcpd.leases';




my $tempfile  = '/tmp/dhcpd.leases';
copy($leasefile,$tempfile) or die "Copy failed: $!";

#my $LocalTZ = DateTime::TimeZone->new( name => 'local' );
my $LocalTZ = '';

open LEASES, "< $tempfile" or die $!;
my @lines = <LEASES>;
close LEASES;


#Get the state of each server
my $readit;
my $line;
#valid failover states
#unknown-state,  partner-down,  normal,  communications-interrupted, resolution-interrupted,  potential-conflict,  recover,   recover-done,   shutdown,   paused, and startup
# seems like I want the last failover statement

my $my_state="cant determine";
my $my_state_time="cant determine";
my $peer_state="cant determine";
my $peer_state_time="cant determine";
my $failover = 0;

foreach $line (@lines){
        if ($line=~/failover peer .*? state {/){
                $readit = 1;
                $failover = 1;
        }
        if ($readit){
                if ($line=~/my\sstate\s(.*?)\sat\s\d\s(.*?)\;/){
                        $my_state = $1;
                        $my_state_time = $2;
                }
                if ($line=~/partner\sstate\s(.*?)\sat\s\d\s(.*?)\;/){
                        $peer_state = $1;
                        $peer_state_time = $2;
                }
        }
        if ($readit && $line=~/^}/){
                $readit = 0;
        }
}

if ($failover){
        $my_state_time = localize($my_state_time);
        my ($mdate, $mtime) = split (/T/,$my_state_time);
        $peer_state_time = localize($peer_state_time);
        my ($pdate, $ptime) = split (/T/,$peer_state_time);

        print "My state is $my_state at $mtime on $mdate\nPartner state is $peer_state at $ptime on $pdate\n";
}else{
        print "This appears to be a stand alone server\n"
}

#Get the leases and their states
my @lease_states;
my $active = 0;
my $lease = 0;
my $ip;
my $mac='                 ';
my $end_date_time;
my $start_date_time;
my $start_time;
my $start_date;
my $name;
my $state;

foreach $line (@lines){
        if ($line=~/lease\s(\d+\.\d+\.\d+\.\d+)/){
                $ip=$1;
                $readit = 1;
                $lease++;
                $name="";
        }
        if ($readit && $line=~/starts\s\d\s(\d+\/\d+\/\d+\s\d+:\d+:\d+)\;/){
                $start_date_time =$1;
  }
        if ($readit && $line=~/ends\s\d\s(\d+\/\d+\/\d+\s\d+:\d+:\d+)\;/){
                $end_date_time =$1;
#print $start_date_time;
#                $start_date_time = localize($start_date_time);
#                ($start_date, $start_time) = split (/T/,$start_date_time);

        }
        if ($readit && $line =~/hardware\sethernet\s(.*?)\;/){
                $mac=$1;
        }
        if ($readit && $line =~/client-hostname\s"(.*?)"\;/){
                $name=$1;
        }
        if ($readit){
                if ($line=~/^\s+binding\sstate\s(.*?)\;/){
                        $state = $1;
                        if ($state eq 'active'){
                                $active++;
                        }
                }
        }
        if ($readit && $line=~/^}/){
                push (@lease_states,"$ip\t$start_date_time\t$end_date_time\t$mac\t$state\t\t$name\n");
                $readit = 0;
        }
}

@lease_states=sort (@lease_states);
my $header=("IP\t\tSTART TIME\t\tEND TIME\t\tMAC\t\t\tSTATE\t\tHOSTNAME\n");
print $header;
print @lease_states;
print "Total leases: $lease\n";
print "Total active leases: $active\n";


sub localize{
# in format 2010/06/01 22:10:01
my $datetime=shift;
my ($date, $time) = split (/ /,$datetime);
my ($hr, $min, $sec) = split (/:/,$time);
my ($yr, $mo, $day)= split (/\//,$date);
#my $dt = DateTime->new(
#                        year   => $yr,
#                        month  => $mo,
#                        day    => $day,
#                        hour   => $hr,
#                        minute => $min,
#                        second => $sec,
#                        time_zone =>'UTC' );

#        $dt->set_time_zone($LocalTZ);
#        return $dt->datetime;
	return $datetime;

# use this to split the out
# ($date, $time) = split (/T/,$dt->datetime);

}

Thanks for the script - in a similar vein to the first post by awfki I had to add in $mac=""; below line 87 to reset the mac address otherwise it looked like one mac address was using all of the spare ip addresses.

@mattpascoe Script works as advertised. Thanks for that! Are you aware of the Text::DHCPLeases module?

@merentitis You have a LG Electronics device. Interesting 😉 To preserve your privacy you should always use a random MAC address based on MAC addresses reserved for documentation as defined by RFC7042. Example: 00:00:5E:00:53:23. You can be targeted using your MAC address as selector!