Set variables in parallel in bash

Question

Here\'s an example program:

#!/bin/bash

for x in {1..5}
do
  output[$x]=$(echo $x) &
done

wait

for x in {1..5}
do
  echo ${output[$x]}
done


        

Answer 1

This

output[$x]=$(echo $x) &

puts the whole assignment in a background task (sub-process) and that's why you're not seeing the result, since it's not propogated to the parent process.

You can use wait to wait for subprocesses, but returning results (other than status codes) is going to be difficult. Perhaps you can write intermediate results to a file, and collect those results after all processes have finished ? (not nice, I appreciate)

Answer 2

If you want to avoid writing files, you can use GNU parallel:

#!/bin/bash
output=(`parallel -k --gnu echo {1} ::: {1..5}`)
for i in ${output[@]}
do
   echo $i
done

The -k is to preserve the order of the output