Thank you very much. I like to learn by example and this is great. I'll be honest I'm trying to understand how the code works as I am still very novice to Perl and programming in general. what do these lines mean?   1+index( <$fh>, $target ) and ++$count while tell( $fh ) < $end; Is this reading the file line by line, returning line number where $target is found, and increasing $count for every time $target is found? Tell function returns the index position just to check end of file? Why couldn't you do while (<$fh>)?

our $T //= 4;
[download]

I couldn't really google two forward slashes so I don't know what this means.

my @threads = map{
    threads->new( \&worker, $filename, $target, $chunks[ $_ ], $chunks
+[ $_+1 ] )
} 0 .. $T-1;
[download]

Ok map will transform arrays, but here it seems like it is assigning 3 threads to @threads? threads->new() creates new thread while passing the worker sub and 4 variables? or is it creating a worker sub and passing those variables to worker?

my $total = 0;
$total += $_->join for @threads;
[download]

this concatenates the thread results? but i don't see where or when the lines with $target were passed back and stored? Thanks again