Using process substitution, only send stderr to process I have this: exec > >( while read line; do echo " stdout: $line"; done ) exec 2> >( while read line; do echo " stderr: $line"; done ) echo "rolo" >&2 echo "cholo" if you run that script, it results in the following output: > stdout: rolo > stdout: stderr: cholo how can I only send stderr to the second process substitution line? I don't get it. I don't understand why this is happening: > stdout: rolo > stdout: stderr: cholo # what lol

You set up the redirections in the wrong order. The standard output of the second process substitution (which prefixes with `stderr:`) has its standard output prefixed by the first process substitution, because it was run afterwards.

Try this instead:


exec 2> >( while read line; do echo " stderr: $line"; done )
exec > >( while read line; do echo " stdout: $line"; done )

echo "rolo"
echo "cholo" >&2


This outputs


stderr: cholo
stdout: rolo


which is what I presume you want.