I hadn't realized that while loops were more efficient than for loops... I just liked the english-like syntax of the foreach loop :) I also usually try to avoid the $_ variable because early in my perl career I always had trouble keeping track of when it was modified.

Anyway, stylistic preferences aside... I made the foreach -> while loop changes you suggested and am getting the same results. With both the original and modified versions of the code the hangup point has moved to just after Marker 2.

I also decided to leave things alone and let the code run its course... and it does decide to continue after about 30 seconds. Which might at least be acceptable as this script will only be running as an hourly cronjob.

I'm also not sure if this really is a memory issue. Here's the output from top while the script is hung up:

PID COMMAND %CPU   TIME   #TH #PRTS #MREGS RPRVT  RSHRD  RSIZE  VSIZE
1279 perl   19.6%  0:02.28   1    10    21   524K  1.42M  1.62M  2.92M
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As you can see, perl isn't using up much memory at all. For those of you wondering about the strange top format... this is on my ibook. Here's the output from top on a linux box:

PID USER PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME COMMAND
16974 root  25   0  1696 1696  1128 R    51.5  0.1   0:02 ip_update.pl
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Well, in the middle of writing this I finally understood what you meant by movind the print DHCPDCONF line and the temporary file... so I made those adjustments and, of course there is no hang. I'm still not sure why it was hanging in the first place, but I guess that is a moot point now.

Thanks for your help :)

Updated Code:

#!/usr/bin/perl

use strict;

#####################################################
# Update MAC-IP pairings for all registered devices #
#####################################################

my %devices;

# Open dhcpd.conf and initialize the %devices hash with all
# registered modems and cpes

open (DHCPDCONF, "dhcpd.conf") or die "Cannot read from file: $!";
while (<DHCPDCONF>)
{
    $devices{lc($1)} = '000.000.000.000'
      if (/#.*#.*#.*# Modem MAC: (\w+:\w+:\w+:\w+:\w+:\w+)/
             or /subclass ".*" 1:(\w+:\w+:\w+:\w+:\w+:\w+)/);
             
}
close DHCPDCONF;

# open leases file and match mac addresses in %devices with active ips
open (LEASES, "dhcpd.leases");
my ($current_ip, $state);
while (<LEASES>)
{

    $current_ip = $1 and next if /^\s*lease (\d+.\d+.\d+.\d+)/;
                  
    $state = $1 and next if /^\s*binding state (\w+)/;
    
    $devices{lc($1)} = $current_ip and
    print lc($1) . " - " . $devices{lc($1)} . "\n" and next if
        (/^\s*hardware ethernet (\w+:\w+:\w+:\w+:\w+:\w+)/
         and $state eq 'active' and exists $devices{lc($1)});    
}
close LEASES;

# substitute old ip with current value
open (DHCPDCONF, "dhcpd.conf") or die "Cannot read from file: $!";
open (DHCPDCONFNEW, ">dhcpd.conf.new") or die "Cannot create file: $!"
+;
while( <DHCPDCONF>)
{
    my $device = lc($1) if /#.*#.*#.*# Modem MAC: (\w+:\w+:\w+:\w+:\w+
+:\w+)/;
    
    s/(#.*#.*# Modem IP: ).*( # Modem MAC: $device)/$1$devices{$device
+}$2/i;
    
    print DHCPDCONFNEW;
    
}
close DHCPDCONF;
close DHCPDCONFNEW;
system("cp dhcpd.conf.new dhcpd.conf");

######## Update LDAP database

# not implemented yet.
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