I think the short answer is simply "Don't use 1-based arrays". There are rare occasions where they're a more natural fit to your data, and so, in this case you can adapt accordingly. Even so, I would still hesitate.

One example is this:

my @months = qw[ Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec ];

So, you can see that when accessing $month[2] that 'Mar' is the result. It's possible to put in a dummy month, such as like this:

my @months = '',qw[ Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec ];

This would work, however, stepping back from the problem, you'll note there's little reason to label January as 1 internally. Look at localtime as an example of how it can be done. In that case, January is month 0.

There are many arguments against 1-based index systems, and I have to concur with most. I'd rather have consistent data structures with offset work done in the interface layer, than vice-versa. For example:

print "Today is in the month ",$month[$calendar_month-1],"\n";

Which is straightforward enough. Wrapped in a function, it becomes even less of an issue:

sub get_month_name
{
     my ($calendar_month) = @_;

     return $month[$calendar_month-1];
}
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