listeners.pl

#!/usr/bin/perl

our %state = ();

for my $line (split /\n/, `netstat -lntup`) 
{
  $line =~ s/\s+$//;
  my $proto, $revq, $sendq, $local, $foreign, $state, $proc;

  if ($line =~ m/^tcp/)
  {
    ($proto, $revq, $sendq, $local, $foreign, $state, $proc) = split /\s+/, $line;
  } 
  elsif ($line =~ m/^udp/)
  {
    ($proto, $revq, $sendq, $local, $foreign, $proc) = split /\s+/, $line;
  }
  else
  {
    next;
  }

  my @addr = split ':', $local;
  my $port = pop @addr;
  my $addr = join ':', @addr;

  my @proc = split '/', $proc;
  my $pid = shift @proc;
  my $service = `systemctl status $pid | head -n1 | cut -d' ' -f2`;

  $service =~ s/\s+$//;
  $state{$proto}{$addr}{$port} = $service;
}

for my $proto ('tcp', 'udp') 
{
  for my $port (sort { $a+0 <=> $b+0 } keys %{$state{$proto}{'127.0.0.1'}})
  {
    unless (exists $state{$proto . '6'}{'::1'}{$port})
    {
      print "$proto $port: listening on v4 localhost but not v6 -- ", $state{$proto}{'127.0.0.1'}{$port}, "\n";
    }
  }

  for my $port (sort { $a+0 <=> $b+0 } keys %{$state{$proto}{'0.0.0.0'}})
  {
    unless (exists $state{$proto . '6'}{'::'}{$port})
    {
      print "$proto $port: listening on v4 global but not v6 -- ", $state{$proto}{'0.0.0.0'}{$port}, "\n";
    }
  }
}