Looks like your questions have been well answered.

I just want to note that it is good that you use strict and warnings. It is even better than you now understand some of what they do. You'll probably recognise these problems immediately next time you encounter them and not have to ask.

But don't stop there. Read the documentation on both pragmas, and play with a few small test scripts trying their variations. Whilst the blanket application of both is generally okay, there are times when it is good to understand their details and be selective in which of their facilities you apply.

Don't be tempted by the false "labour saving" of modules replace that those two short lines with one long one.

You might also look into the differences between warnings and -w on the shebang line. For instance, you might conclude that the extra bells and whistles of the former are largely redundant most of the time, if you, like most people, strive to write your code so that it avoids the situations that raise the warnings; rather than opt to silence them by force.

And realise that on those occasions when you do choose to silence a warning, no warnings works just fine in conjunction with -w