You might want to look at the localtime() documentation to get an idea. It also shows an example of using the POSIX module for doing time.

Recall that year is the difference from 1900, so years 2000 and beyond are 100+, rather than being 2-digit numbers. Just add back the 1900 and you should be okay, I would think. Something along the lines of the following might work:

sub local_yyyymmdd {
  my $time = shift || time();
  my ($year, $month, $mday) = (localtime($time))[5,4,3];
  $year += 1900;
  $month++;
  return sprintf "%04d-%02d-%02d", $year, $month, $mday;
}
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HTH.

Update: (08-Dec-2003) Changed format for sprintf from "%4d-%2d-%2d" to "%04d-%02d-%02d" to force leading zeros. (Thank you, ysth, for noting that.)