Use of uninitialized value $destination_IP in string ne at...

##</code><code>##

ns1.sina.com.cn. 80800 IN A 202.106.184.166

##</code><code>##

clear in_list flag
FOR each line in the data file
  IF line matches first line of a list THEN
    extract IP
    save IP as source
    set in_list flag
  ELSE
    IF in_list flag set THEN
      SWITCH line
        CASE line matches second list line
          ignore it
        CASE line matches list-address
          save addresses, indexed to current source
        CASE default (i.e. no longer in list)
          clear in_list flag
      ENDSWITCH
    ENDIF
  ENDELSE
ENDFOR

##</code><code>##

#! perl
use strict;
use warnings;

my $line1_re = qr! ^ Traceroute: \s+ .* \s+ (\S+) $ !x;
my $line2_re = qr! ^ traceroute !x;
my $destn_re = qr! ^                                # start of line
                   \s*                              # optional whitespace
                   \d+                              # sequence number: nnn
                   \s+                              # whitespace
                   (?:                              # EITHER
                        (?: \d{1,3} \. ){3} \d{1,3} #   IP address: nnn.nnn.nnn.nnn
                        |                           # OR
                        \* \s+ \* \s+ \*            #   * * *
                   )
                 !x;

my (%ipToRoute, $source_IP, $in_tracing);

while (my $line = <DATA>)
{
    chomp $line;

    if ($line =~ /$line1_re/)
    {
        $source_IP  = $1;
        $in_tracing = 1;
    }
    elsif ($in_tracing && $line !~ /$line2_re/)
    {
        if ($line =~ /$destn_re/)
        {
            $line =~ s/ ^ \s+ //x;
            my $destination_IP = (split /\s+/, $line)[1];
            push @{ $ipToRoute{$source_IP} }, $destination_IP
                unless $destination_IP eq '*';
        }
        else
        {
            $in_tracing = 0;
        }
    }
}

foreach (keys %ipToRoute)
{
    my $final_destination = @{ $ipToRoute{$_} }[-1];
    printf "Destination to %s but reached %s\n",
            $_, $final_destination unless $_ eq $final_destination;
}

__DATA__
Traceroute: 22 1291136399 1291136393 1291136393 LocalDNS home.china.com.cn 221.204.248.107
traceroute to 221.204.248.107 (221.204.248.107), 30 hops max, 60 byte packets
 1  134.2.173.254  0.170 ms  0.191 ms  0.185 ms
etc.

##</code><code>##

Destination to 92.123.72.112 but reached 92.123.72.0
Destination to 78.108.81.20 but reached 217.106.1.146
Destination to 208.78.244.38 but reached 208.78.244.0