Bash: how do I pipe stdout and stderr of one process to two different processes?

Question

I have a process myProcess1 that produces both stdout and stderr outputs. I want to pipe the two output streams into two different downstream processes, myProcess2 and myProcess3 , that will massage the data and then dump the results into two different files. Is it possible to do it with a single command? If not, the 2nd best would be running two separate commands, one to process stdout , the other stderr . In this case, the first run would simply be:

myProcess1 | myProcess2 > results-out.txt

What would be a similar command to process stderr ? Thx

Answer 1

Without fancy games something like this should work:

{ myProcess1 | myProcess2 > results-out.txt; } 2>&1 | myprocess3 > results-err.txt

With fancy games (which do not work in /bin/sh , etc.) you could do something like this:

myProcess1 2> >(myprocess3 > results-err.txt) | myProcess2 > results-out.txt

Answer 2

A named pipe or two would work well for this, but you'll probably find it easiest to do with multiple terminal windows.

In one terminal window:

mknod stdout.pipe p
mknod stderr.pipe p
myProcess1 > stdout.pipe 2> stderr.pipe

In a second window:

myProcess2 < stdout.pipe

And in a third:

myProcess3 < stderr.pipe

Using background processes and some other tricks, you could do it all in one window, but keeping the output of your secondary processes separated would be another challenge...

You could eliminate one of the named pipes (and thus one of the extra windows) with either of these:

myProcess1 2> stderr.pipe | myProcess2

or

{ myProcess1 > stdout.pipe; } 2>&1 | myProcess3