Question

How do I get the correct return code from a unix command line application after I’ve piped it through another command that succeeded?

In detail, here’s the situation :

$ tar -cEvhf - -I ${sh_tar_inputlist} | gzip -5 -c > ${sh_tar_file}  --  when only the tar command fails $?=0
$ echo $?
0

And, what I’d like to see is:

$ tar -cEvhf - -I ${sh_tar_inputlist} 2>${sh_tar_error_file} | gzip -5 -c > ${sh_tar_file}
$ echo $?
1

Does anyone know how to accomplish this?

Answer 1

Here is a general solution using only POSIX shell and no temporary files:

Starting from the pipeline:
foo | bar | baz

exec 4>&1
error_statuses=`((foo || echo "0:$?" >&3) |
        (bar || echo "1:$?" >&3) | 
        (baz || echo "2:$?" >&3)) 3>&1 >&4`
exec 4>&-

$error_statuses contains the status codes of any failed processes, in random order, with indexes to tell which command emitted each status.

# if "bar" failed, output its status:
echo $error_statuses | grep '1:' | cut -d: -f2

# test if all commands succeeded:
test -z "$error_statuses"

# test if the last command succeeded:
echo $error_statuses | grep '2:' >/dev/null