How to use nohup with curly braces?

Question

I try to run the following command (ref.) using nohup, which basically separates stdout and stderr into two processes.

{ foo 2>&1 1>&3 3>&- | sed -u 's/^/err: /'; } 3>&1 1>&2 | sed -u 's/^/out: /'

The foo script is like below.

#!/bin/bash
while true; do
   echo a
   echo b >&2
   sleep 1
done

This is the test result.

$ nohup { foo 2>&1 1>&3 3>&- | sed -u 's/^/err: /'; } 3>&1 1>&2 | sed -u 's/^/out: /' >/dev/null 2>&1 &
-bash: syntax error near unexpected token `}'

Try: `nohup bash -c "{ foo 2>&1 1>&3 3>&- | sed -u 's/^/err: /'; } 3>&1 1>&2" | sed -u 's/^/out: /' >/dev/null 2>&1 &` — anubhava, Oct 24 '22 at 03:19
Or instead use [this answer](https://stackoverflow.com/a/49299040/2868801) which works fine with nohup. — dave_thompson_085, Oct 24 '22 at 04:00
What's the goal of this: `... | sed -u 's/^/out: /' >/dev/null 2>&1` ??? Why did you run `sed` for dropping his output?? Maybe `nohup foo &>/dev/null &` will do your job! — F. Hauri - Give Up GitHub, Oct 24 '22 at 05:56

score 1 · Accepted Answer · answered Oct 24 '22 at 03:21

1

That's syntatically impossible. But you can wrap your {} in a sh -c cmd:

nohup sh -c 'foo 2>&1 1>&3 3>&- | sed -u "s/^/err: /"'

Notice I change the single quote for sed to double quote.

answered Oct 24 '22 at 03:21

DannyNiu

1 Answers1