I prefer to use the POSIX function strftime. An example of this would be:

use strict;
use warnings;
use POSIX qw(strftime);
print strftime("%Y%m%d", localtime()), "\n";
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Here are descriptions of the format flags. The man page is from FreeBSD, but most of the flags are standards-compliant, so it's pretty much a moot point.

I find this preferable because it requires significantly fewer lines of code and reuses library functionality.