open2() is from the module IPC::Open2.
From `perldoc IPC::Open2`:
This whole affair is quite dangerous, as you may block forever. It assumes it's going to talk to something like bc, both writing to it and reading from it. This is pre­sumably safe because you "know" that commands like bc will read a line at a time and output a line at a time. Pro­grams like sort that read their entire input stream first, however, are quite apt to cause deadlock.

In reply to Re: confused (and frustrated) about stdin/out by kwoff
in thread confused (and frustrated) about stdin/out by smackdab

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