In trying to solve a problem setting up iptables on my Linux gateway box, I wrote a Perl script to display netfilter activity in real-time. Every second, it grabs output from the iptables list utility, including counters (which are then zeroed). It displays this data with extraneous lines removed, highlighting the lines with non-zero packet counts in color. It's designed to run in an xterm window and uses ANSI escape sequences to control the text. To be effective, the xterm window needs to be at least as high as the output, else scrolling will ruin the visual effect. Also, the code may be iptables version-dependent, as it matches certain keywords for the formatting. Once started, it can be stopped with a ctl-C, which will restore some of the display settings. Herewith is the code: 
#!/usr/bin/perl
use strict;
use warnings;
my @types = qw/nat mangle filter/;
$SIG{INT} = sub{print "\e[?25h\e[u"; exit}; 
print "\e[40;37m\e[2J\e[?25l";
while (1) {
  print "\e[0;0H";
  my %output = map {$_ => scalar `iptables -t $_ -L -v -Z`} @types;
  foreach my $type (@types) {
    print "\e[01;34m------", uc($type), '-' x (73 - length($type)), "\
+n";
    $output{$type} =~ s/ pkts[^\n]*\n(\n|Zeroing)/$1/gs;
    foreach my $line (split /\n/, $output{$type}) {
      next if $line =~ m/^Zeroing/ || $line eq '';
      print $line =~ m/^\s*(\d+)/ || $line =~ m/(\d+) packets/
        ? ($1 > 0 
          ? ($line =~ m/DROP|DENY|REJECT/
            ? "\e[01;40;31m" 
            : "\e[01;40;32m")
          : "\e[00;40;37m")
        : "\e[00;40;33m";
      print "\e[K$line\e[01;40;37m\n"
    }
  }
  print "\e[s";
  sleep 1
}

[download]

In reply to Real-time Iptables Monitor by Dr. Mu

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.