But you should be using the three parameter version of open and lexical file handles

No, in this case, two parameter open, and a file glob is just fine.

Note for instance that lexical file handles have been with us since 5.000. It wasn't until they also got to be autovivifying that they got more popular.

I think it's for starters (actually, everyone) far more important to get their programs correct, before worrying about the nuances between 2-arg and 3-arg open, or globs and autovivifying filehandles.