alt Hacker NewsUseless use of cat error/award
But also | isnt a redirection, it takes stdout and pipes it to another program.
So, if you want stderr to go to stdout, so you can pipe it, you need to do it in order.
bob 2>&1 | prog
You usually dont want to do this though.
The point is that the order in which that is processed is not left to right.
First the | pipe is established as fd [1]. And then 2>&1 duplicates that pipe into [2]. I.e. right to left: opposite to left-to-right processing of redirections.
When you need to capture both standard error and standard output to a file, you must have them in this order:
It cannot be: Because then the 2>&1 redirection is performed first (and usually does nothing because stderr and stdout are already the same, pointing to your terminal). Then > file redirects only stdout.But if you change > file to | process, then it's fine! process gets the combined error and regular output.