Ok, let's say we have a usecase - a job on Jenkins CI that needs to start a background process, remember PID of the process, pass the PID to some later cleanup. And we need something that will work on Linux and on Mac OS X (yes, even this OS can behave polite).
So 1st, let's start a process and remember it's PID. This is done via $! shell environment variable. The $! variable will have PID of latest started process. So here is an example:
nohup tail -f /var/log/syslog > /tmp/$BUILD_TAG.log & export LOGGER_PID=$!
# $BUILD_TAG - is an environment variable provided by Jenkins CI, it has unique job execution identifier
2nd, let's remember the PID
echo -e "LOGGER_PID=$LOGGER_PID" > /tmp/$BUILD_TAG
3rd, let's use the PID and send SIGTERM to the process if it is still alive. We'll wrap it to a shell script.
#!/bin/bash
. /tmp/$BUILD_TAG # read to LOGGER_PID env variable
kill_proc(){
local pid_alive=`ps ax| awk '{print $1}' | grep -e "^$LOGGER_PID$" >>/dev/null; echo $?`;
# ps ax| awk '{print $1}' - will print to stdout PIDs without surrounding spaces
# grep -e "^$LOGGER_PID$" >>/dev/null; - will search for the PID, ^ and $ are important, just in case our PID is a substring of some other PID on system
# echo $? - will echo exit code of last command
if [ $pid_alive -eq 0 ]; then
kill $LOGGER_PID; # sending SIGTERM to the process
sleep 10;
else
echo "Proc with PID $LOGGER_PID already terminated"
fi;
}
kill_proc;
