#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;
use Fcntl qw(:flock); # import LOCK_* and SEEK_END constants
use Fcntl qw(SEEK_SET SEEK_CUR SEEK_END); #SEEK_SET=0 SEEK_CUR=1 ...

my @doc_write;
my @array;
my $file = "test.txt";

sub add {
    open (DATA, "+<", $file)
	or die ("Could not open file: ".$file.". $!\n");

    flock(DATA, LOCK_EX)
	or die "Could not lock '".$file."' - $!\n";

    if (-z "".$file."") {
	print DATA "0\n";
    }

    while( @doc_write = <DATA> ) {
	
	chomp @doc_write;

	seek(DATA , 0 , SEEK_SET)
	    or die "Cannot seek - $!\n";
	
	truncate(DATA, 0);
	
	my $range = 50;
	my $minimum = 100;

	my $random_number = int(rand($range)) + $minimum;
	my $time = time();

	my $packet = join (' ' , $time , $random_number);

	push(@doc_write , $packet);

	print Dumper (\@doc_write);

	foreach $_ (@doc_write) {
	    print DATA $_ . "\n";
	}

	close (DATA)
	    or die "Could not close '".$file."' - $!\n";

	return $packet;
	
    } # End of While (<DATA>)

} # End of sub add

while (sleep 1) {

    my $losses = &add();
    
    print "Added:" .$losses. "\n";

}

##</code><code>##

while (sleep 1) {
read all data into an array...
extract last element...
process it..
write to a secondary file the extracted data for comparison purposes..
}