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
}
