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

Answer 1

Here is some code that I have been running, that seems to do exactly what you want. Just insert ./a.sh and ./b.sh where appropriate:

# Start the processes in parallel...
./script1.sh 1>/dev/null 2>&1 &
pid1=$!
./script2.sh 1>/dev/null 2>&1 &
pid2=$!
./script3.sh 1>/dev/null 2>&1 &
pid3=$!
./script4.sh 1>/dev/null 2>&1 &
pid4=$!

# Wait for processes to finish...
echo -ne "Commands sent... "
wait $pid1
err1=$?
wait $pid2
err2=$?
wait $pid3
err3=$?
wait $pid4
err4=$?

# Do something useful with the return codes...
if [ $err1 -eq 0 -a $err2 -eq 0 -a $err3 -eq 0 -a $err4 -eq 0 ]
then
    echo "pass"
else
    echo "fail"
fi

Note that this captures the exit status of the script and not what it outputs to stdout. There is no easy way of capturing the stdout of a script running in the background, so I would advise you to use the exit status to return information to the calling process.