How to redirect running process output from pipe to something else?

Question

Is there any way to redirect stdout (1) from that "pipe" (I don't know exacly how I suppose interpret this, I will be glad if someone could explain how to treat this, or give me some read on this) to some other output, eg. file or terminal?

-bash-4.2$ ls -l /proc/11/fd
total 0
lrwx------ 1 us sudo 64 Sep 24 11:26 0 -> /dev/null
l-wx------ 1 us sudo 64 Sep 24 11:26 1 -> pipe:[20619]
l-wx------ 1 us sudo 64 Sep 24 11:26 2 -> pipe:[20620]
lrwx------ 1 us sudo 64 Sep 24 11:26 3 -> socket:[30376]
lr-x------ 1 us sudo 64 Sep 24 11:26 4 -> /dev/null
l-wx------ 1 us sudo 64 Sep 24 11:26 5 -> pipe:[30639]
lrwx------ 1 us sudo 64 Sep 24 11:26 6 -> socket:[27522]

Answer 1

Not in a clean or portable way. You have to attach with a debugger like gdb, open some the destination file and dup it into fd 1. As with

gdb -p <PID> -batch -ex 'call dup2(open("<PATH>", 2), 1)'

That pipe:[digits] is an "anonymous" pipe, as created by cmd | cmd shell construct.

However on Linux it's not really anonymous, since you can open it via /proc/<PID>/fd/<NUM>. So you have another option (which is guaranteed to wreak even more havoc than using gdb): open the other side of the pipe, kill whatever program is reading from it, and cat it somewhere else. Stupid example:

% while sleep 1; do TZ=Zulu date; done | wc -c &
[1] 26727
% ps
  PID TTY          TIME CMD
20330 pts/1    00:00:00 bash
26726 pts/1    00:00:00 bash     # this the while ... done process
26727 pts/1    00:00:00 wc
26745 pts/1    00:00:00 sleep
26746 pts/1    00:00:00 ps
% ls -l /proc/26726/fd/1
... /proc/26726/fd/1 -> 'pipe:[1294932]'
% exec 7</proc/26726/fd/1        # open the other side of the pipe
% kill 26727                     # kill wc -c
% cat <&7
Fri 24 Sep 2021 01:25:52 PM UTC
Fri 24 Sep 2021 01:25:53 PM UTC
Fri 24 Sep 2021 01:25:54 PM UTC
...