The POSIX module also provides the strftime() function, which is very convenient to use in this case as well:

use strict;
use POSIX qw(strftime);

sub local_yyyymmdd {
  my ($time) = shift || time;
  return strftime( '%Y-%m-%d', localtime($time));
};
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Documentation on strftime is pretty scarce, as it is the C function of the same name, but the DateTime module has a similar function which takes similar parameters in the format string.

Updated: Added dashes thanks to ysth, added paragraph about the documentation

perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ;    # The  
$d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider
($c = $d->accept())->get_request(); $c->send_response( new   #in the
HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' #  web
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DateTime also has a routine ymd that outputs the date in exactly the format he needs :-)

PerlJam

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.)

sub local_yyyymmdd {
  my $time = shift || time();
  my ($year, $month, $mday) = (localtime $time)[5,4,3];
  return sprintf "%04d-%02d-%02d", $year+1900, $month+1, $mday;
}
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use POSIX qw/strftime/;

sub local_yyyymmdd {
    return strftime "%Y-%m-%d", localtime($_ || time());
}
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...
return sprintf "%04d-%02d-%02d",
                $year+1900,$month+1,$mday
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