Yeah, let's avoid reading from STDIN, or avoid writing to STDOUT or STDERR.

Oh, c'mon. Oversight due to generalization, updated post.

And to your other points: Yes, warnings are easy to notice in programs with very little output. And as noted elsewhere, there may or may not have been only a 'used once' warning in the actual code. And whether or not you catch the error in closing a handle that's already closed, it's better to catch the error at 'compile' time rather than runtime. Also note, "IT'S NOT MY CODE", and I consider myself lucky if others check the return value of open and include $! in the error message. If they start checking the return value of close, I might die of shock.