Here's one I like:

my $ymd = sub{sprintf '%04d%02d%02d',
    $_[5]+1900, $_[4]+1, $_[3]}->(localtime);
[download]

The interesting thing about it is the dataflow aspect, how you take a stream of variables and modify them on the way to their destination. Having this particular tool in you toolbox can come in handy from time to time.