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Old 10-28-2014, 03:57 AM   #1
plotino
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how to kill a background job from within a shel script


Hello
I have written a scritp that starts a process in backgroung
(using the ampersend character).
After the script is run, the job is started, but at the moment i have to use 'ps' commmand to get the PID and use manually the kill command.
I would like to automate the exit action for the process.

How to include the close command for the process from within the script?

thanx

plotino
 
Old 10-28-2014, 04:02 AM   #2
rigor
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Hi plotino!

If you are using bash, the variable $! contains the pid of the last background process that was run.

If you are using some other shell, please let us know which one it is.


HTH.
 
Old 10-28-2014, 04:11 AM   #3
pan64
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yes, the solution is $!:
Code:
start_background_process &
BG_PID=$!

... do whatever you want ...

# kill your background process:
kill -s <signal> $BG_PID
# or alternatively you may use:
kill -s <signal> %1
# wait for completition:
wait $BG_PID
# or
wait %1
 
Old 10-28-2014, 04:11 AM   #4
plotino
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thanks rigor.
im using bash.
so the question now is how to exploit the variable $! at the end of the script to close the backgrounded process?
can i associate it to some keys? i dont know how ...


thanks pan64,
the point is that running the scipt, you come back to the shell, where the running and backgroundede process gives some log infos.
during this, at any time, i would like to stop the process for example with a key combination

Last edited by plotino; 10-28-2014 at 04:21 AM.
 
Old 10-28-2014, 04:18 PM   #5
ondoho
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less elegant, but works:
Code:
killall $(pidof start_background_process)
obviously requires a unique name for the process.
 
Old 10-28-2014, 05:40 PM   #6
rigor
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plotino,

I realize that there can be a tendency to think that abstracting a question from the details surrounding it, asking it in the abstract, may be simplifying the issue, but sometimes it actually makes getting the answer more difficult, or at least more of a protracted procedure. Especially because the details may change the answer.

As for the more specific situation that you are now describing, a trivial example of a potential solution, depending on whether or not there are additional relevant details:

Code:
trap 'kill $!'  2

sleep 900 &

sleep 60
when I run the above bash script, then use my "Interrupt" key to kill the foreground sleep, the trap hook will execute the kill command to kill the background sleep.

These and other mysteries can be solved by running:

Code:
man bash
 
Old 10-29-2014, 04:05 AM   #7
plotino
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thanks rigor,
you are right. need more details.
my script is..

Code:
"process" &
command1
command2

so, it put process in bg, run command1 and command2, and after it exits.

Adding

Code:
 trap "kill $!" 2
"process" &
command1
command2
i need to not exit from the script to be able to kill the bg process, isnt'it?

so i have to add a wait(forever) instruction at the end.

this my supposition, please tell me if im right .

ciao

plotino
 
Old 10-29-2014, 04:07 AM   #8
pan64
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So as I posted, you can write
wait <pid>
or
wait %1
 
Old 10-30-2014, 04:18 AM   #9
plotino
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Quote:
Originally Posted by pan64 View Post
So as I posted, you can write
wait <pid>
or
wait %1
ok thank you.

i have resolved with this:

Code:
trap 'kill $!' 2
<process> &
command1
command2
sleep 10000
ciao

plotino
 
Old 10-30-2014, 01:23 PM   #10
haertig
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What is your ultimate goal? From your description, it appears that you are starting a process that assumedly will take a while to run. So you start it in the background. Fair enough. Then you run two other commands that I assume completely quickly. When those last two commands are done, you want to then go kill the original backgrounded process, whether it's done or not? Or possibly the background process runs forever and generates information that is consumed by the latter two processes, and once those latter two processes are complete, you no longer need the backgrounded process?

I don't understand your goal. If you want to kill that backgound process right after the two other commands have completed, a solution has already been suggested. But if you want to wait until that background process has completed, then kill it, that's what I'm not understanding. If it's already completed, then it's done, dead, in its grave already. You don't have to kill it a second time.
 
  


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