How safe is it to use EXPORT in bash scripts when using GNU Parallel?

Question

How safe is it to use export in bash scripts when using GNU Parallel?

I have a parent script. parent.sh

(echo child.sh & echo child_two.sh) || parallel bash

wait
if [[ "$STATUS1" == "0" && "$STATUS2" == "0" ]];
then
    //continue
else
    //stop the process
fi

child.sh

Getting the STATUS1 based on another process

export STATUS1

child_two.sh

Getting the STATUS2 based on another process

export STATUS2

Is is safe to use export and does the value of STATUS1 & STATUS2 get resrt eveytime it is being run?

Answer 1

Environments variables are passed into the child processes, not the other way.

If you want to transmit information to the parent process, then you want to put this data into one file per child and cat those files after the child processes have ended.

tmp=$(mktemp -d)
child.sh $tmp/file & child_two.sh $tmp/file_two
wait 
cat $tmp/* 
rm $tmp -rf

If you want to make some optimization, feel free to use a higher level language.

Answer 2

I think you will benefit from looking into parset https://www.gnu.org/software/parallel/parset.html

$ parset myvar 'echo do stuff with {};(exit {}); echo $?' ::: 0 0 1 2 3 0 0
$ echo "${myvar[3]}"

Answer 3

You can't do that because export is setting a variable in a process that is about to be discarded; the parent can never see it.

However, assuming you're using bash, you also don't need to:

child.sh &
child_two.sh &

wait -n
STATUS1=$?
wait -n
STATUS2=$?

The wait -n returns the exit status from one of the processes, and repeating it gets the status from the other.

The only gotcha with this recipe is that there's no way to know which status came from which process (if you need that read up on bash Job Control).