Child process passing parent a status code

[Brian Pyle]

I'm using /usr/bin/sh, and am trying to figure out a way to manage a number of child procceses. I need to pass exit statuses back to the parent (managing) from the children. I have looked at trap, but it appears that is a one way from parent to child, not the other way. I was trying to avoid a file or fifo if possible. Anybody know of a way to pass info back to the parent?

[Steven E. Protter]

return 0
exit 0

for good status codes

return 1
exit 1

for bad.

There is a system for the various codes if you want to be all official.

The methodology above passed the code back from the child to the parent, if the parent is waiting. Whether or not this works depends on how the child was launched.

SEP

[A. Clay Stephenson]

A child can certainly send a signal to a parent process that the parent can trap BUT the only thing that will be known is the signal number itself not an exit status.

One option is to use the wait command.
child.sh &
CHILDPID=${!}
...
...
...
wait ${CHILDPID}

The wait will block until the child finished and report its status.

Trying to export a variable from the child to the parent absolutely will not work.

[Brian Pyle]

My apologies, I left out a very crucial piece of info on this. I want the child to run in the background :)

Thanx

[A. Clay Stephenson]

In that case, my cut at this would be:

1) Capture the child pid using ${!}.

child.sh &
CHILDPID=${!}

The child will write its status to a temp file
based upon it's process ID ${$}.
e.g. /var/tmp/X${$}.txt
and just before exiting send a signal to its parent process using ${PPID}.
e.g. kill -s 16 ${PPID}

The parent would have a trap on signal 16 (or the agreed upon signal) to then read /var/tmp/X${CHILDPID}.txt for the status information and then remove the temp file.

This will give you a mechanism for asynchronously handling multiple child processes while continuing to do useful task in the parent. All the child processes could share a command signal but the operation should be quick so that no signals are ignored while processing an existing one.

[Brian Pyle]

Thanx for the help. Even though Clay's last example is probably what I'm going to use, I was really hoping somebody had a way to do this without writing a file. I've contemplated using some socket communica via perl, but would also like to avoid that if possible. Thought maybe somebody had a silver bullet :)

Thanx Again

Brian Pyle

[Peter Nikitka]

Hi,

the exit-Status of the 'wait'-command is that of the child, so:
child &
wait $!
child_exit=$?

Peter