Get exit code of a background process

user_190338 0
Viewed 191306

I have a command CMD called from my main bourne shell script that takes forever.

I want to modify the script as follows:

  1. Run the command CMD in parallel as a background process (CMD &).
  2. In the main script, have a loop to monitor the spawned command every few seconds. The loop also echoes some messages to stdout indicating progress of the script.
  3. Exit the loop when the spawned command terminates.
  4. Capture and report the exit code of the spawned process.

Can someone give me pointers to accomplish this?

shell process unix linux
13 Answers

My solution was to use an anonymous pipe to pass the status to a monitoring loop. There are no temporary files used to exchange status so nothing to cleanup. If you were uncertain about the number of background jobs the break condition could be [ -z "$(jobs -p)" ].

#!/bin/bash

exec 3<> <(:)

{ sleep 15 ; echo "sleep/exit $?" >&3 ; } &

while read -u 3 -t 1 -r STAT CODE || STAT="timeout" ; do
    echo "stat: ${STAT}; code: ${CODE}"
    if [ "${STAT}" = "sleep/exit" ] ; then
        break
    fi
done
user_124042260

how about ...

# run your stuff
unset PID
for process in one two three four
do
    ( sleep $((RANDOM%20)); echo hello from process $process; exit $((RANDOM%3)); ) & 2>&1
    PID+=($!)
done

# (optional) report on the status of that stuff as it exits
for pid in "${PID[@]}"
do
    ( wait "$pid"; echo "process $pid complemted with exit status $?") &
done

# (optional) while we wait, monitor that stuff
while ps --pid "${PID[*]}" --ppid "${PID[*]}" --format pid,ppid,command,pcpu
do
    sleep 5
done | xargs -i date '+%x %X {}'

# return non-zero if any are non zero
SUCCESS=0
for pid in "${PID[@]}"
do
    wait "$pid" && ((SUCCESS++)) && echo "$pid OK" || echo "$pid returned $?"
done

echo "success for $SUCCESS out of ${#PID} jobs"
exit $(( ${#PID} - SUCCESS ))
user_113656710
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