looks_like_number you can use to test whether anything has the format Perl uses for numbers

More specifically, if looks_like_number($x) returns false then perl should issue the "isn't numeric" warning for $x, but if looks_like_number($x) returns true then there should be no "isn't numeric" warning for $x.

This correlation doesn't hold for recent blead releases (including the current 5.21.8) wrt some 'inf' strings, and perhaps some 'nan' strings too.
But it should now be restored for 5.21.9.

That this correlation ought to exist might be no more than *my* opinion, though it seems obvious to me (and matches past behaviour afaik).
If someone has an example of it not holding in perl-5.20.x, I'd be interested to learn of it.

Cheers,
Rob