# instead of this:
my @lines = <DATA>;

# do something like this:

while my $line (<DATA>) {
...
}
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If you can more clearly explain what this code is supposed to do, we might be able to find a much more straightforward solution. As it is, the code seems to be doing the same thing over again several times in different ways before printing its final results.

Alan

Just to further explain what I am tryint to achieve. We currently manage acouple hundred subnets at my job. Each Monday morning, we get ARP cache dumps from all of our routers sent to us. People send us requests for IP addresses and DNS names. There are network admins that are notorious for not returning IP addresses.

What I am trying to do, is take the last few months worth of ARP information (that is the tail -250000... command. It's jsut an approximation). We use that to determine which IPs have had no activity for a while and we remove the allocation from our records and notify the admin that we had it assigned to that we have reclaimed the address.

Thanks for the input!

perl -e 'print reverse qw/o b n a e s/;'

If you're concerned about memory usage, you shouldn't read the entire file at once. Read it line by line and count the IPs in a hash, so you don't get duplicated entries. And, of course, use strict, but I guess you knew that already :) Anyhow, here's a snipped that came to my mind:

#!/usr/bin/perl -w

use strict;

my $subnet = '192.168.87';
my %data = ();
# precompile regex for performance..
my $regex = qr#^($subnet\.\d+)#;

# read file line by line
while (my $line = <DATA>)
{
    chomp($line);

    if ($line =~ $regex)
    {
            $data{$1}++;
    }
    elsif ($debug)
    {
            print STDERR "Didn't match: $line\n";
    }
}
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If you really do want to stick to your own code, your line is better written as (it's not very nice either..):

my @matches = grep { m/$regex/ } @lines;
($_) = m/$regex/ foreach @matches;
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Regards,
-octo-

I'll give this a try. I was trying to be elegant and do things faster than brute forcing my way line by line, but I guess you see where that got me... :-(

Yea, I know I really should have been using strict and i felt like an idiot posting the code without it (thus the warning up top). Thanks for your input!

when I clean up the code (and am using strict like I should be), I will repost the code.

perl -e 'print reverse qw/o b n a e s/;'

#!/usr/bin/perl -w

  use strict;
  use vars qw/ $opt_s /;

  use Getopt::Std;
  use Net::Netmask;

  my $subnet;
  my %data = ();
  my $ARP = '/tmp/arp.bak';

  getopt('s');

  if (defined($opt_s) && $opt_s ne '') {
    $subnet = $opt_s;
  } else {
    help();
  }

  my $block = new Net::Netmask($subnet);
  if (defined($block->{'ERROR'})) { die "Invalid subnet/mask combinati
+on."}

  my @range = $block->enumerate();

  #We need to get our temp file
  system `tail -250000 /tmp/arp > $ARP`;

  #Open the file and read it line by line
  open(FH, $ARP) || die ("Couldn't open the arp file $ARP");
  while (<FH>)
  {
    if (/^((?:\d{1,3}\.){3}\d{1,3})/)
    {
      if ($block->match($1)) { $data{$1}++; }
    }
  }
  close FH;

  #I need to specifically remove the network, gateway and broadcast
  #addresses since we don't care about those.

  #First remove from enumeration array
  shift @range;  #Network Address
  shift @range;  #Gateway Address
  pop @range;    #Broadcast Address

  #Now remove from the IP's found in the ARP cache
  delete $data{$block->base()};
  delete $data{$block->nth(1)};
  delete $data{$block->broadcast()};

  my @matches = keys %data;

  #Compare the array of matched IPs to the enumerated Netblock
  my @intersection = my @difference = ();
  undef %data;
  foreach my $element (@matches, @range) { $data{$element}++ }
  foreach my $element (keys %data) {
      push @{ $data{$element} > 1 ? \@intersection : \@difference }, $
+element;
  }

  #Now I'd like to sort the IPs (a little Schwartzian Transform action
+ here...)
  my @sorted = map { join '.', unpack 'N*', $_ }
               sort
               map { pack 'N*', split /\./ }
               @difference;

  print "Addresses that are candidates for reclaim in:\n";
  print $block->desc(), "\n\n";
  print join("\n",@sorted), "\n";

  sub help {
    print <<'HELP';
     You must supply a valid subnet.
     Acceptable formats are as follows:

      192.168.1.0/24            <--- The preferred form.
      192.168.1.0:255.255.255.0
      192.168.1.0-255.255.255.0

    syntax: arpscan.pl -s 192.168.1.0/24
HELP
   exit(1);
  }
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