How do I create or test for NaN or infinity in Perl?

Personally, I would use Math::BigFloat (or BigInt) for anything that is going to touch infinity of NaN.

Why reinvent the wheel with a hack solution when there are already modules that do the job?

Use Data::Float from CPAN. It exports the following functions:

• float_is_infinite()
• float_is_nan()
• ...

And contrary to the others half-working solutions posted here, it has a testsuite.