I'm writing a small module for checking whether or not a phone number is correct, and I'd like to be able to return informative error messages, such as "Missing area code" and similar. But how do I do this in a neat manner?

The function is to be used in a web form, and it returns a cleaned-up version of the phone number on success (or the empty string, if the user didn't enter a phone number).

I'm guessing that what I want to do when the number is incorrect in some way is to return undef, and set $@ to something explanatory (which then could be given as user feedback in the webform).

But how do I do this nicely? Redefine die() (add some kind of __DIE__ hook?) or write my own sub to call on failure, which returns and sets $@ (so that my checks may still read e.g. /^$/ or fail "no number"?

I read perlmodstyle ("Error handling and messages"), but I could find no answer to my question there.

In reply to How to return an appropriate error from module? by zrajm

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