system doesn't mess with any of the file handles passed to the child. If caller.pl is called interactively, so is ask_input.pl.

But why are you using -t? You need to get your answer from somewhere. You can't test if you're going to receive an answer from a terminal, so that's the last place you should check. You should base whether you prompt or not based on the presence or absence of the answer elsewhere (e.g. argument, config file).

In reply to Re^2: Altering Behavior of a Script by ikegami
in thread Altering Behavior of a Script by bichonfrise74

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