CODEWITHSUNDEEP
bashshellprocesstry-catch
toriningen
toriningen

Reputation: 7462

How to get exit status of piped command from inside the pipeline?

Consider I have following commandline: do-things arg1 arg2 | progress-meter "Doing things...";, where progress-meter is bash function I want to implement. It should print Doing things... before running do-things arg1 arg2 or in parallel (so, it will be printed anyway at the very beginning), and record stdout+stderr of do-things command, and check it's exit status. If exit status is 0, it should print [ OK ], otherwise it should print [FAIL] and dump recorded output.

Currently I have things done using progress-meter "Doing things..." "do-things arg1 arg2";, and evaluating second argument inside, which is clumsy and I don't like that and believe there is better solution.

The problem with pipe syntax is that I don't know how can I get do-things' exit status from inside the pipeline? $PIPESTATUS seems to be useful only after all commands in pipeline finished.

Maybe process substitution like progress-meter "Doing things..." <(do-things arg1 arg2); will be fine, but in this case I also don't know how can I get exit status of do-things.

I'll be happy to hear if there is some other neat syntax possible to achieve same task without escaping command to be executed like in my example.

I greatly hope for the help of community.

UPD1: As question seems not to be clear enough, I paraphrase it:

I want bash function that can be fed with command, that will execute in parallel to function, and bash function will receive it's stdout+stderr, wait for completion and get its exit status.

Example implementation using evals:

progress_meter() {
    local output;
    local errcode;

    echo -n -e $1;

    output=$( {
        eval "${cmd}";
    } 2>&1; );
    errcode=$?;

    if (( errcode )); then {
        echo '[FAIL]';
        echo "Output was: ${output}"
    } else {
        echo '[ OK ]';
    }; fi;
}

So this can be used as progress_meter "Do things..." "do-things arg1 arg2". I want the same without eval.

Upvotes: 0

Views: 903

Answers (3)

holygeek
holygeek

Reputation: 16185

Have your scrips in the pipeline communicate by proxy (much like the Blackboard Pattern: some guy writes on the blackboard, another guy reads it):

  1. Modify your do-things script so that it reports its exit status to a file somewhere.

  2. Modify your progress-meter script to read that file, using command line switches if you like so as not to hardcode the name of the blackboard file, for reporting the exit status of the program that it is reporting the progress for.

Upvotes: 0

Dimitre Radoulov
Dimitre Radoulov

Reputation: 28000

I'm not sure I understand what exactly you're trying to achieve, but you could check the pipefail option:

 pipefail
                              If  set,  the  return value of a pipeline is the
                              value of the last (rightmost)  command  to  exit
                              with  a non-zero status, or zero if all commands
                              in the pipeline exit successfully.  This  option
                              is disabled by default.

For example:

bash-4.1 $ ls no_such_a_file 2>&- | : && echo ok: $? || echo ko: $?
ok: 0
bash-4.1 $ set -o pipefail
bash-4.1 $ ls no_such_a_file 2>&- | : && echo ok: $? || echo ko: $?
ko: 2

Edit: I just read your comment on the other post. Why don't you just handle the error?

bash-4.1 $ ls -d /tmp 2>&- || echo failed | while read; do [[ $REPLY == failed ]] && echo failed || echo "$REPLY"; done  
/tmp
bash-4.1 $ ls -d /tmpp 2>&- || echo failed | while read; do [[ $REPLY == failed ]] && echo failed || echo "$REPLY"; done  
failed

Upvotes: 1

n. m. could be an AI
n. m. could be an AI

Reputation: 119877

Why eval things? Assuming you have one fixed argument to progress-meter, you can do something like:

#!/bin/bash
# progress meter
prompt="$1"
shift

echo "$prompt"

"$@"    # this just executes a command made up of 
        # arguments 2, 3, ... of the script
        # the real script should actually read its input, 
        # display progress meter etc.

and call it

$ progress-meter "Doing stuff" do-things arg1 arg2

If you insist on putting progress-meter in a pipeline, I'm afraid your best bet is something like

(do-things arg1 arg2 ; echo $?) | progress-meter "Doing stuff"

Upvotes: 2

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