Yes they could, but it would change the behaviour of the routine. For instance, 86401 would produce 1d1s instead of 1d0h0m1s.

Which may be what you want (ultra-compact!), but it wasn't what I needed.

update: re your update: you're quite right. Adding the $res into the format string is a bit too clever by half. I completely overlooked .= . It's feedback like this that make Perl Monks such a useful site.

g r i n d e r