#!/perl/bin/perl.exe

use strict;
use warnings;

use LWP::Simple;
use MIME::Lite;

my $reflector = "http://your.webhost.com/cgi-bin/ipreflect.cgi";
my $logfile = "ip.log";


# Get IP from an IP reflector server.
my $ip = get $reflector;
chomp $ip;

my $now = localtime;

$ip = "Reflector server down." unless (
  $ip =~ m/^\d+\.\d+\.\d+\.\d+$/ or
  $ip =~ m/Not Available/i );

# Read log to determine if the IP changed since last test.
my $ip_changed = "";
if ( -e $logfile ) {
    open my $inlog, "<", $logfile or
        die "Can't read logfile.\n$!";
    while ( <$inlog> ) {
        next unless eof;
        chomp;
        my $last_ip = ( split /\s+=>\s+/ )[1];
        $last_ip =~ s/\*$//;
        $ip_changed = ( $last_ip ne $ip ) ? "*" : "";
    }
    close $inlog;
} else {
    # If the logfile doesn't exist, assume IP changed.
    # This forces an update to the remote server anytime
    # the logfile is deleted.  Remember, for a fresh start
    # at both ends, just delete the local logfile.
    $ip_changed = "*";
}


# Update log.
open my $log, ">>", $logfile or 
  die "Can't open output logfile.\n$!";
print "$now => $ip$ip_changed\n";          # Screen output.
print $log "$now => $ip$ip_changed\n";     # Logfile output.     
close $log or die "Couldn't close output file.\n$!";


# If the IP changed, send the new IP to remote server via email.
if ( $ip_changed and $ip =~ m/^\d+\.\d+\.\d+\.\d+$/ ) {
    my $msg = MIME::Lite->new(
        From     =>'your@email.address',
        To       =>'your.email@address.on.web.host',
        Subject  =>"[IP Log] $now",
        Data     =>"Updated: $now\nIP: $ip\n"
    );
    MIME::Lite->send(   'smtp', 
                        "your.isp.smtp.server", 
                        Timeout => 60 
    );
    $msg->send;
}