Hello maheshkumar, and welcome to the Monastery!

i am getting 80800

Yes, you’re getting the wrong answer there, but before that you are also getting 136 warnings of the form:

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

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which should act as a red flag that your logic is wrong somewhere. Never ignore warnings! They are there to help you.

Now, the problem with your script is that it’s finding lines like this:

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

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which come after the list of IP addresses you are interested in. So, you need some way of turning off the search when the list has ended. Here is one possible algorithm:

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

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Here is an implementation in Perl:

#! 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 whitesp
+ace
                   \d+                              # sequence number:
+ nnn
                   \s+                              # whitespace
                   (?:                              # EITHER
                        (?: \d{1,3} \. ){3} \d{1,3} #   IP address: nn
+n.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.co
+m.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.

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With the data you supplied, this outputs:

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

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as required. Note: For improved readability, I have extracted the regular expressions using the qr operator, and annotated the third one because of its complexity.

HTH,

Athanasius <°(((>< contra mundum

In reply to Re^3: Printing first and last line by Athanasius
in thread Printing first and last line by maheshkumar

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