how to wait on multiple background processes and check exit status in bash

wait.sh

#!/bin/bash

FAIL=0

echo "starting"

./sleeper 2 0 &
./sleeper 2 1 &
./sleeper 3 0 &
./sleeper 2 0 &

for job in `jobs -p`
do
    echo $job
    wait $job || let "FAIL+=1"
done

echo $FAIL

if [ "$FAIL" == "0" ];
then
    echo "YAY!"
else
    echo "FAIL! ($FAIL)"
fi

that's a nice workaround.. but, using just the wait command (without passing the process ID) would have worked too? So that, it waits for all the background process to get complete.

./sleeper 2 0 &
./sleeper 2 1 &
./sleeper 3 0 &
./sleeper 2 0 &

wait

Please let me know your thoughts.

(I got here from your blog post - http://jeremy.zawodny.com/blog/archives/010717.html)

The idea is to know how many processes failed. You can't do that without the for loop.

you can also use trap, something like this:

#!/usr/bin/env bash

set -m # allow for job control
EXIT_CODE=0;  # exit code of overall script

function foo() {
   echo "CHLD exit code is $1"
      echo "CHLD pid is $2"
      echo $(jobs -n)

   if [[ $? > 0 ]]; then
      echo "at least one test failed";
      EXIT_CODE=1;
   fi
}

trap 'foo $? $$' CHLD

DIRN=$(dirname "$0");

commands=(
    "{ echo "foo" && exit 4; }"
    "{ echo "bar" && exit 3; }"
    "{ echo "baz" && exit 5; }"
)

clen=`expr "${#commands[@]}" - 1` # get length of commands - 1

for i in `seq 0 "$clen"`; do
    (echo "${commands[$i]}" | bash) &   # run the command via bash in subshell
    echo "$i ith command has been issued as a background job"
done

# wait for all to finish
wait;

echo "EXIT_CODE => $EXIT_CODE"
exit "$EXIT_CODE"

# end

but how could you know the first subprocess in loop is the one finished first, if the later ones in loop finished early, what is the return code

that's a nice workaround.. but, using just the wait command (without passing the process ID) would have worked too? So that, it waits for all the background process to get complete.

./sleeper 2 0 &
./sleeper 2 1 &
./sleeper 3 0 &
./sleeper 2 0 &

wait

Please let me know your thoughts.

(I got here from your blog post - http://jeremy.zawodny.com/blog/archives/010717.html)

So nice, thank you! It works in my script.