I'm sure there are shorter, much more elegant ways of doing this (hire a monk:), plus in a multi-interface system, you'd want more info about which "device" from the arp table.. but, here's a basic approach..

#!/usr/bin/perl -w

# kernels 2.4.x /proc/net/arp

use strict;

 my $ipad;
my $macad;
  my @arp;

if ( -r "/proc/net/arp" ) {
   open(ARP,"</proc/net/arp");
   @arp = <ARP>;
   close(ARP);
} else {
     die("Cannot access arp in proc $!");
}

foreach my $linein ( @arp ) {
  chomp($linein);
  next if $linein =~ /IP/i;
  $ipad  = (split(/\s+/,$linein))[0];
  $macad = (split(/\s+/,$linein))[3];
  print "IP address $ipad has MAC Address $macad\n";
}
[download]

to start with.. definitely not portable to Windows or BSD, just linux

You could also split up each record getting a value for each field with something like

($ipad,$macad,$hwtype,$flags,$mask,$device) = split(/\s+/,$linein);
[download]

-hsinclai