bash - Execute multiple shell scripts concurrently

Question

I want to do the following things:

• Execute multiple shell scripts (here 2 scripts) concurrently.

• Wait until both scripts finish

• Dump return value of each script

However, main.sh does not work as expected.

main.sh

#!/bin/bash

ret1=`./a.sh` &
ret2=`./b.sh`

if [ "${ret1}"="" -a "${ret2}"="" ]; then
   sleep 1
else
   echo ${ret1},${ret2}
end

a.sh

#!/bin/bash
sleep 10
echo 1

b.sh

#!/bin/bash
sleep 5
echo 2

Answer 1

If you have GNU Parallel http://www.gnu.org/software/parallel/ installed you can do this:

parallel -j0 '{}; echo $?' ::: a.sh b.sh

I have a suspicion that you want the exit code to check if one of them failed, and that you actually do not care what the precise exit code was. In that case you can do:

parallel -j0 ::: a.sh b.sh || echo one or both of them failed

If it is sufficient to get the error code of the last that failed:

parallel -j0 --halt 1 ::: a.sh b.sh; echo $?

Maybe you would like to kill a.sh if b.sh finishes early but fails:

parallel -j0 --halt 2 ::: a.sh b.sh; echo $?

You can install GNU Parallel simply by:

$ (wget -O - pi.dk/3 || lynx -source pi.dk/3 || curl pi.dk/3/ || 
   fetch -o - http://pi.dk/3 ) > install.sh
$ sha1sum install.sh | grep 883c667e01eed62f975ad28b6d50e22a
12345678 883c667e 01eed62f 975ad28b 6d50e22a
$ md5sum install.sh | grep cc21b4c943fd03e93ae1ae49e28573c0
cc21b4c9 43fd03e9 3ae1ae49 e28573c0
$ sha512sum install.sh | grep da012ec113b49a54e705f86d51e784ebced224fdf
79945d9d 250b42a4 2067bb00 99da012e c113b49a 54e705f8 6d51e784 ebced224
fdff3f52 ca588d64 e75f6033 61bd543f d631f592 2f87ceb2 ab034149 6df84a35
$ bash install.sh

Watch the intro videos for GNU Parallel to learn more: https://www.youtube.com/playlist?list=PL284C9FF2488BC6D1

Print the cheat sheet: https://www.gnu.org/software/parallel/parallel_cheat.pdf