Symmetric commands: tee

[Poshi]

tee is another command that works in one way but not the other. It allows you to send the data stream to a file or a command. But I cannot see any construct that allows us to inject the results from a command into the data stream.
The closest thing I can imagine is system(), but it returns the whole stdout blob with no easy way of feeding it into the data stream (you can always postprocess it, cut by new lines, extract fields and emit data but...).

This is just food for though. I don't need the functionality, but it triggers an alarm in me seeing this imbalance.

[johnkerl]

@Poshi agreed.

I've thought about this on & off for a year or two. You're right, system() pays the fork-and-exec overhead on every invocation, which doesn't scale.

In analogy with the concept of 'coroutine' in programming languages, I like the idea of a 'coprogram'. Question though about output-buffering (an arbitrary program can't be relied on to fflush every output line), and boundaries (do we insist the coprogram be writing 'records' one per line or not)? Etc.

Anyway I share your interest & I'd love to get some brainstorming going on how to make this happen ...