#!/usr/bin/perl
use strict;
use warnings;

open (my $junkfile, '>', "junkfile");
my $junk = '';

for my $first_byte (0 .. 255) {
    for my $second_byte (0 .. 255) {
        $junk .= pack('CC', $first_byte, $second_byte);
        $junk .= "\0" x 2;
    }
}
print $junkfile $junk;
close $junkfile;

open(my $orig, '<', "junkfile") or die $!; 
seek( $orig, 256, 0);
print_locations("Locations after seeking ORIG to 256: ");

my $correct;
read($orig, $correct, 8);
print_locations("Locations after reading 8 bytes from ORIG: ");

my @bytes = unpack('C*', $correct);
print "ORIG read these bytes: @bytes\n";

open(my $dupe, "<&", $orig) or die $!; 
print_locations("Locations immediately after duping: ");

seek( $dupe, 256, 0);
print_locations("Locations after seeking DUPE to 256: ");

seek($orig, 120, 0);
print_locations("Locations after seeking ORIG to 120: ");

my $useless;
read($orig, $useless, 20);
print_locations("Locations after reading 20 bytes from ORIG: ");

my $test;
read($dupe, $test, 8);
print_locations("Locations after reading 8 bytes from DUPE: ");

@bytes = unpack('C*', $test); 
print "DUPE read these bytes: @bytes\n";

sub print_locations {
    my $label = shift;
    print "$label\n    ";
    print "ORIG " . tell($orig) . "  "; 
    print "DUPE ";
    print defined $dupe ? tell($dupe) : "not valid";
    print "\n";
}