[oak perl] The mysterious "undef"

[Zed Lopez]

One aspect of use warnings is that you get a "Use of uninitialized
value" warning if you try to use an undef value.

Perl will auto-convert undef to '' if you use it as a string, and you
won't hear about it if you don't have warnings on.

Always turn warnings on for non-trivial scripts. (There are reasons to
turn it off for selected code blocks, and super-experts like Damian
Conway often do a lot of stuff with it off... but until you're a
super-expert and you _know_ you have a very good reason for having it
off for a specific piece of code, leave it on.)

This isn't a pointless issue: you should and must understand Perl's
automatic conversions, or its DWIMmery won't do what you mean.

On Fri, 18 Mar 2005 11:10:22 -0500, Sandy Santra <santranyc at yahoo.com> wrote:
> I keep seeing "undef" mentioned in the llama book.
> 
> I've tried to define a variable as not having a value, theoretically being
> "undef," but when I use the print command, I never see "undef" print to my
> screen; nothing prints at all.
> 
> I wanted to learn the different between a zero value and undef because the
> llama book keeps saying there is one.  Is this a pointless issue to pursue?
> 
> Clarification greatly appreciated.  Thanks.
> 
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