while(<>) {
        $timestring = $_ =~ $some_regexp;
        $min = &get_nr_of_mins ($timestring);
        if(/start:/) {
                /split/ and ++$split;
                /filter/ and ++$filter;
        }
        elsif(/finish:/) {
                /split/ and --$split;
                /filter/ and --$filter;
        }
        if($min % $granularity == 0) {
                print "$time: $split, $filter\n";
        }
}