Shell Programming and Scripting

Hi,

I have a shell script that creates 2 parallel processes. When I press ctrl+c, i want the parallel process to get killed as well.

Code:

#!/bin/bash



cmd1="script1.py" 
cmd2="script2.py" 


${cmd1} & 
pid1=$!
echo ${pid1} 


${cmd2} & 
pid2=$!
echo ${pid2} 


trap 'kill ${pid1} ${pid2}; echo "this works"' INT

When I use the ps command and check, I dont see the pid1 and pid2 getting killed? Kindly help me out.

Thanks.

The script will run and quit without receiving any sort of interrupt, leaving the processes behind.

Your trap command is faulty. It does not mention what signals it is trapping and has problems with the single quote characters:

Maybe try this. Note that I have twiddled with your quote characters so that the values of $pid1 and $pid2 get expanded. Any variable between single quote characters does not get expanded:

Code:

trap INT "kill ${pid1} ${pid2}; echo 'this works'"

Please remember to post what Operating System and version you have and what Shell you are running (okay it is bash). Without this basic information any response is pure guesswork.

@Methyl,

This is the info of the system that I am using:

Code:

Linux version 2.6.16.60-0.58.1.1290.1.PTF.600981-smp (geeko@buildhost) (gcc version 4.1.2 20070115 (SUSE Linux)) #1 SMP Wed Dec 2 12:27:56 UTC 200

And when I change the trap according to what you have posted, I get the following:

Code:

trap: kill 5218 5219; echo 'this works': invalid signal specification

---------- Post updated at 03:37 PM ---------- Previous update was at 03:35 PM ----------

@Corona,

Yeah, that is exactly what is happening. I am trying to find a solution to that. Since I am fairly new to coding in linux, I am not sure how to kill the subprocesses.

Anybody out there with matching SUSE who can try this trap and correct the syntax?

Your process doesn't get a signal unless it's sent one, so you're looking for the wrong thing.

Try trap "do something" EXIT instead.

That system is pretty old. I've got SUSE 12.x running on one of my boxes and this works for me:

First a little 'run it' script that does something (probably sleep):

Code:

#/usr/bin/env ksh 
# (could be bash)

echo "$$: running $@"
"$@"
echo "$$: done"
exit 0

If we don't see the done message, we assume it was killed. I did add a trap to run-it to verity, but the timing generated messages after the shell prompt and it was confusing.

Code to invoke the processes. the big problem, as Corona pointed out, is that the initial script doesn't wait for the asynch processes it just exits. Wait added at end to allow it to actually trap the interrupt.

Code:

#!/bin/bash

run_it sleep $1 &
pid1=$!
echo ${pid1}  
  
run_it sleep $1 &
pid2=$! 
echo ${pid2} 
  
trap 'kill -15 ${pid1} ${pid2}; echo "killed: $pid1 $pid2"' INT
wait   # very important to wait for the asynch processes if they are to be killed with ctl-c

The quoting is as it was on the original post; the $pid1 and $pid2 variables are expanded when the trap is executed. This allows the trap to be set before the processes are invoked; this allows for the starting several sets of processes, killing the most recently started pair when interrupted, without having to reset the trap for each. There are arguments pro and con for this I am sure, but not really the point here.

Finally, I always thought the syntax for trap is:

Code:

trap [-p] 'command' signal [...]

Specifying the signal before the command string would result in a syntax error.