linux：为什么如果你通过管道将 ps 传送到 grep，grep 过滤器正在处理输出？ 管道是如何工作的？

Question

With a typical command like ps aux |grep foobar why grep foobar process is in output?

I was thinking that ps aux output was passed to grep to filter the lines by the pattern in grep argument but at the time you execute ps aux grep is still not executed (at least it's what I was supposing, I am wrong for sure), is executed later.

How does pipe works then?

Answer 1

The reason is simple:

1. OS starts the grep process (as the pipe target).
2. OS starts the ps , which finds grep running .
3. OS connects the standard output of ps to the standard input of grep .