Example 17-9. backsniff

  #!/usr/bin/perl -w
  # backsniff - log attempts to connect to particular ports
  use strict;
  use Sys::Syslog qw(:DEFAULT setlogsock);
  use Socket;
  # identify my port and address
  my $sockname       = getsockname(STDIN)
                       or die "Couldn't identify myself: $!\n";
  my ($port, $iaddr) = sockaddr_in($sockname);
  my $my_address     = inet_ntoa($iaddr);
  # get a name for the service
  my $service = (getservbyport ($port, "tcp"))[0] || $port;
  # now identify remote address
  $sockname          = getpeername(STDIN)
                           or die "Couldn't identify other end: $!\n";
  ($port, $iaddr)    = sockaddr_in($sockname);
  my $ex_address     = inet_ntoa($iaddr);
  # and log the information
  setlogsock("unix");
  openlog("sniffer", "ndelay", "daemon");
  syslog("notice", "Connection from %s to %s:%s\n", $ex_address,
          $my_address, $service);
  closelog( );