Modern::Perl is not needed. If you are on a "low" Perl version, like 5.10 or earlier, you may want to replace say by print.

Also see Yes, even you can use CPAN for installing Perl modules.

you may be right , but even i changed the say to print but there are compilation error at line 1 indicating Modern::Perl . i will be so thankful if you guide me in any alternative way. THANKS

Have you tried removing that line?

Also read perlsyn and use, maybe.

I notice you've been advised (multiple times) to just remove the offending line. I suspect, though, that you may get similar messages with the other two modules.

When there's a task like yours, it's good to first see if there's a module for it (or some components of it), as modules can help avoid 'reinventing the wheel,' are often mature and well-tested, and can reduce development time and programmatic errors. Some, however, may have to work with the Perl environment as is, with no option to install modules.

Given the above, see the modified script below (that's not a subroutine):

use strict;
use warnings;

my ( $file, $loop, %seen ) = 'junk.txt';

open my $fh1, '<', $file or die "Unable to open $file: $!";
while ( my $fileName = <$fh1> ) {
    chomp $fileName;

    print "The packet traversed this path in $fileName:\n";

    open my $fh2, '<', $fileName or die "Unable to open $fileName: $!"
+;
    while ( my $fileLine = <$fh2> ) {
        $fileLine =~ /(\d+\.\d+\.\d+\.\d+)/ or next;
        $loop++ if ++$seen{$1} > 1;
        print "$1\n";
    }

    close $fh2;
    print "\n";
}

close $fh1;

print "** Routing Loop Detected **\n" if $loop;
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