[inkyoto]

> Each of those components executes in parallel, with the intermediate results streaming between them. You get a similar effect with coroutines.

Processes run in parallel, but they process the data in a strict sequential order: «grep» must produce a chunk of data before «sed» can proceed, and «sed» must produce another chunk of data before «xargs» can do its part. «xargs» in no way can ever pick up the output of «grep» and bypass the «sed» step. If the preceding step is busy crunching the data and is not producing the data, the subsequent step will be blocked (the process will fall asleep). So it is both, a pipeline and a chain.

It is actually a directed data flow graph.

Also, if you replace «haystack.txt» with a /dev/haystack, i.e.

  grep needle < /dev/haystack | sed 's/foo/bar/g' | xargs wc -l

and /dev/haystack is waiting on the device it is attached to to yield a new chunk of data, all of the three, «grep», «sed» and «xargs» will block.