OT: how to get shell status of first pipe shell command (when fail), not that of the last one

[Dario Lesca]

When I concatenate 2 or more shell command with pipe (|), I get only
the status of last one.

For example: "some-cmd | logger -t "some-cmd messages:"; echo $?"

If "some-cmd" fail with status !=0 I get always status of last one, in
this case 0

In my case if the first command fail, I must send a warning message

A more simple example is: "false | true"

I want get status 1, of first command (false), not 0 (true)

I have also try "sh -e -c 'false || exit 2|true'; echo $?" but I get
always 0

How to I get first status and break the chains of pipes ?

Many thanks

Hi.

On Mon, 05 Nov 2018 15:00:04 +0100 Dario Lesca wrote:
> For example: "some-cmd | logger -t "some-cmd messages:"; echo $?"
> If "some-cmd" fail with status !=0 I get always status of last one, in
> this case 0
> In my case if the first command fail, I must send a warning message
> A more simple example is: "false | true"
> I want get status 1, of first command (false), not 0 (true)

Use the PIPESTATUS array:

false | true; echo ${PIPESTATUS[0]}
    1

[Dario Lesca]

Il giorno lun, 05/11/2018 alle 15.15 +0100, [e-mail]
ha scritto:
> Use the PIPESTATUS array:
>     false | true; echo ${PIPESTATUS[0]}    1
> --francis

Thank Francis!I did not know this kind of useful parameter

[John Mellor]

On Mon, 2018-11-05 at 15:00 +0100, Dario Lesca wrote:
> When I concatenate 2 or more shell command with pipe (|), I get only
> the status of last one.
>
> For example: "some-cmd | logger -t "some-cmd messages:"; echo $?"
>
> If "some-cmd" fail with status !=0 I get always status of last one,
> in this case 0
>
> In my case if the first command fail, I must send a warning message
>
> A more simple example is: "false | true"
>
> I want get status 1, of first command (false), not 0 (true)
>
> I have also try "sh -e -c 'false || exit 2|true'; echo $?" but I get
> always 0
>
> How to I get first status and break the chains of pipes ?

Assuming that your shell is bash:
    set -o pipefail

[Andrej Podzimek]

> When I concatenate 2 or more shell command with pipe (|), I get only the status of last one.
>
> For example: "*some-cmd | logger -t "some-cmd messages:"; echo $?*"
>
> If "*some-cmd*" fail with status !=0 I get always status of last one, in this case 0
>
> In my case if the first command fail, I must send a warning message
>
> A more simple example is: "false | true"
>
> I want get status 1, of first command (false), not 0 (true)
>
> I have also try "*sh -e -c 'false || exit 2|true'; echo $?*" but I get always 0
>
> How to I get first status and break the chains of pipes ?

Bash has a built-in array called PIPESTATUS (documented in man bash) containing exit statuses from *all* stages of the previous pipeline. With PIPESTATUS you can check how each individual pipeline stage terminated. Here's a toy example:

# Random good-for-nothing pipeline with exit codes 55, 44, 33, 22, 11 and 0:
(exit 55;) | (exit 44;) | (exit 33;) | (exit 22;) | (exit 11) | :

# Inspecting and copying PIPESTATUS ... caution, this has a caveat:
# You can expand PIPESTATUS only once per pipeline. Copy it if need be.
pipestatus=("${PIPESTATUS[@]}")

# Now you can check how each pipeline stage terminated!
for stage in "${!pipestatus[@]}"; do
   echo "Stage ${stage} exited with status ${pipestatus[stage]}."
done

Output from the cycle above:
Stage 0 exited with status 55.
Stage 1 exited with status 44.
Stage 2 exited with status 33.
Stage 3 exited with status 22.
Stage 4 exited with status 11.
Stage 5 exited with status 0.

That's it. Enjoy!
Andrej

[Dario Lesca]

Il giorno mar, 06/11/2018 alle 00.40 +0100, Andrej Podzimek via users
ha scritto:
> Bash has a built-in array called PIPESTATUS

Good also "set -o pipefail" , but for me this array is better because
it gives me more control over which command fails

Many Tanks to all