Thank your for your comment and insights. Yes, my example is only the tip of the iceberg as you showed very clearly concerning robustness. But I think there is a little difference between allowing a filename of "0" and messing up a default behaviour of perl by changing special variables.

But anyways: Be sure I don't condemn anybody for how he or she is coding. The only person I do is myself.

And you have to admit that I haven't used the term error anywhere because it's the right of the programmer to write a function where "0" is not a valid filename in his sence.

I initiated this thread because on the one handside newcomers are said to study at least top rated CPAN code to learn from it and on the other handside is a framework like a fundament which shouldn't have litte fissures.

McA

P.S.: A ++ for showing all the implications while coding in perl5.