# Subroutine that takes a filename of the form DDMM.xxx and returns
# a filename of the form DDMMYYYY.xxx.

sub alt_name {
    local $_ = shift;
    die "Illegal filename" unless my ($dd, $mm, $ext) = /^(\d\d)(\d\d)
+.(.+)$/;

    my ($day, $month, $year) = (localtime) [3 .. 5];
    $year += 1900;
    $month ++;

    if ($mm > $month || $mm == $month && $dd > $day) {
        # Assume file dates from last year.
        $year --;
    }

    sprintf "%02d%02d%04d.%s" => $dd, $mm, $year, $ext;
}
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As you see, the code doesn't add an 'A' or some other letter, but adds a year. It assumes that a date with a later month than the current month, or with a later day if the month is the current month is a file from last year (probably mostly important during your first run in January), else it's a file from this year. Of course, this scheme will fail if you wait more than a year between batches. But if you do, files in your Xwords directory might be overwritten anyway.

The reason I picked a year and not a letter is that otherwise you need to keep some state to see when you need to switch to the next letter. Now we just borrow the state from your OSses clock.

-- Abigail