use threads ;
use feature "say";
use warnings;

my $input_file = "text";				#Contains a single lined string without any newline character
open my $hd, "<", $input_file or die "Couldn't open '$input_file' - $!";
my $text=<$hd>;
chomp($text);

my $window=5;						#Length of the window
my $i=0;
LOOP:seek $hd,$i,0;					#Here seek and read give us the first $window lengthed substing runned over loop
read ($hd,my $substring,$window);
my %hash;
if(length($substring)==$window)				
{
	$hash{$substring}=$i;				#$substring pushed into a hash, here I have avoided array has there may be repeated substrings in the $text
	$i++;
	goto LOOP;
}

my $count = keys %hash;
my $j=0;

foreach my $pattern (keys %hash)
{
	if($j<=$count)
	{
		my $thr="thread".$j;
		$$thr=threads->create(\&position,$text,$pattern);
		$j++;
	}
}

for($ii=0;$ii<=$count;$ii++)
{
	$thr="thread".$ii;
	print $thr,"\n";
	$$thr->join();
}

sub position
{
	my ($text,$pattern) = @_ ;
	
	my $offset = 0;

	print "\n$pattern ($window)\n";
	print '~' x $window,"\n";
	
	my $pos=index $text,$pattern,$offset;
	
	while ($pos != -1) 
	{
		print $pos+1," to ",$pos+$window,"\n";
		$offset = $pos + 99;
    	$pos = index($text, $pattern, $offset);
    }
}