You use looks_like_number from Scalar::Util. That is the best you can get it. Please note that you can't create a real is_number because there's no good answer to that. Something can look like a number but be a string, or be a string and a number simultaneously (see dualvar in aforementioned module and the special variable $!.

It is possible to see if a variable has a number, though. See if the IOK or NOK flags is set. I'm not telling how this can be done, because I think it's wrong to do this. It only leads to implicit trouble. Look for Devel modules. It's better to let the caller decide how something should be interpreted. In case of DBI placeholders, I'd like different placeholders for different types. I have always wondered why it wasn't more sprintf-like.