#!/usr/bin/perl# This scripts checks whether the interface to the internet is up,# and exits with a non-zero status if not.# You can use it in a timed shell script to restart your network# interface if it drops.# This script takes an optional argument - the depth into the network# to your ISP's router. This defaults to one.# If a router is found at the specified depth, this script will exit# with a code of zero and report success to standard error. Uncomment# the line at the bottom to also write the address of the router to# standard output.# Otherwise it will exit with a code of one and report an error to# standard error.# This script uses the traceroute command available from:#   http://ee.lbl.gov/# The one that comes with your UNIX system will probably also work -# with fewer arguments (see below).# It uses either a reserved address or private address as the destination# so that the routers will route packets to their default gateway, or drop# them. Packets will go no further than your ISP's routers. The objective# is to have minimal impact.# location of traceroute binary my $traceroute = '/usr/local/traceroute/sbin/traceroute';#my $traceroute = '/usr/bin/traceroute';# set addressmy $address;# sample reserved addresses# - see http://www.iana.org/assignments/ipv4-address-space$address = '197.0.0.1';#$address = '219.0.0.1';#$address = '220.0.0.1';#$address = '221.0.0.1';#$address = '222.0.0.1';#$address = '223.0.0.1';# sample private addresses# - see http://ietf.org/rfc/rfc1918.txt#$address = '172.16.1.1';#$address = '10.1.1.1';#$address = '192.168.1.1';# Perl modulesuse strict;# distance to routermy $depth = shift;$depth = 1 if ! defined $depth;# traceroute exists?if (! -x $traceroute) {  print STDERR "could not execute traceroute binary $traceroute\n";  exit 2;}# number of hops for traceroutemy $hops = $depth;$hops = 2 if $hops < 2;# run traceroutemy $cmd = "$traceroute -I -n -q 1 -w 3 -m $hops $address 2> /dev/null";#my $cmd = "$traceroute -n -m $hops $address 2> /dev/null";#print STDERR $cmd . "\n";my $output = `$cmd`;my $status = $? >> 8;#print STDERR $output;# executed OK?if ($status ne 0) {  print STDERR    "invalid status code: $status\n" .    "command: $cmd\n";  exit 2;}# split output into linesmy @lines = split(/\n/, $output);#foreach my $line (@lines) {#  print STDERR $line . "\n";#}# got line at routers depth?my $line = $lines[$depth - 1];if (! defined $line) {  print STDERR "router not found at depth $depth - too deep\n";  print STDERR $output;  exit 1;}#print STDERR $line . "\n";# split line into tokens$line =~ s/^\s+//;my ($hopnum, $hopaddr) = split(/\s+/, $line);#print STDERR "hopnum = $hopnum\n";#print STDERR "hopaddr = $hopaddr\n";if (! defined $hopnum or ! defined $hopaddr) {  print STDERR    "invalid response from traceroute\nhop number and addess not found\n";  print STDERR $output;  exit 2;}# depth matches?if ($hopnum ne $depth) {  print STDERR "invalid response from traceroute\nincorrect hop number\n";  print STDERR $output;  exit 2;}# timed out?if ($hopaddr eq '*') {  print STDERR "router not found at depth $depth - timed out\n";  print STDERR $output;  exit 1;}# report addressprint STDERR "router address $hopaddr found at depth $depth\n";#print STDOUT $hopaddr;