korn shell scripting - how to check return codes of background processes?

[Paul Ammirata]

I'm running a script that executes three processes (not necessarily shell script) in the background and then waits for them to complete. If any one of those processes exits with a non-zero return code I want to detect this and exit the script; otherwise I want to continue executing the script.

How can I do this? (i.e. check the return code of the completed background processes)

I've written the following test code, but I'm not able to detect any non-zero return codes.

#! /bin/ksh
# main script
backgroundprocess1 & #hardcoded to exit with 2
backgroundprocess2 & #hardcoded to exit with 0
backgroundprocess2 & #hardcoded to exit with 0
wait
echo $? # always displays 0

###################

#backgroundprocess1
sleep 5
exit 2

###################

#backgroundprocess2
sleep 5
exit 0

###################

#backgroundprocess3
sleep 5
exit 0

[James R. Ferguson · Accepted solution]

Hi Paul:

See this thread:

http://forums.itrc.hp.com/cm/QuestionAnswer/1,1150,0x5bb76af52b04d5118fef0090279cd0f9,00.html

...JRF...

[Robin Wakefield]

Hi Paul,

A small word of caution - the wait in a korn-shell can give erratic results (see the last comment in James' link). If at all possible, use a bourne-shell, this gives 'sensible' results.

Rgds, Robin.

[Bill Thorsteinson]

Consider writing a subroutine to execute a command
and record its status in a status file. Something like:

sub stat_command {
statfile=$1
shift
$($*; echo \$? > $statfile) &
}

You can then check the contents of the
statfiles when the tasks complete.