my $sub = sub {
                my ($data, $res, $proto) = @_;
                
                # either write directly to file or push onto an array
                $filename ? print FILE $data : push(@res_lines, $data);
                
                # increment total length
                $data_recved += length $data;
                
                if ($already_drew_percentage) {                
                    # erase an old sign and draw a new one
                    
                    print "\b" x 9, sprintf('%03d%% done',
                         (($data_recved / $res->content_length) * 100));
                } else {
                    # draw the first percentage
                    
                    printf('%03d%% done',
                         (($data_recved / $res->content_length) * 100));
                   $already_drew_percentage = 1;
           }
};