How to write a shell script to find PID and Kill - linux

Question

I am trying to write a script that looks for the PID of another script that ran previously. Once it finds that PID it then sends a kill signal.
I can find the PID but the kill signal does not process, I get a return message that it is not a PID.
Here is what I am doing:
#!/bin/bash
PID=`ps -eaf | grep "start.sh" | awk '{print $2}'`
echo "$PID"
if [[ -z "$PID" ]];
then(
echo "Start script is not running!"
)else(
kill -9 $PID
)fi
The script it is trying to kill starts many other scripts so I am hoping that killing start.sh will kill all child processes.

Answer 1

When you run
ps -eaf | grep "start.sh" | awk '{print $2}'
you create a subshell with the word start.sh in it. grep will then pick up on its own process and the start.sh one so you will get two PIDs back.
This means when you are trying to kill both start.sh and the
ps -eaf | grep "start.sh" | awk '{print $2}'
processes. The start.sh will die but the other will no longer exist so can't be killed, so it gives you an error.
If you were to split up the commands you might have better luck:
PIDS=$(ps -eaf)
PID=$(echo "$PIDS" | grep "start.sh" | awk '{print $2}')

Answer 2

Try using pgrep:
PID=$(pgrep yourprocesname)

Answer 3

You could use pidof rather then ps -ef
PID=`pidof start.sh | awk '{print $1}'`
echo "$PID csshst will be stopped"
if [[ -z "$PID" ]]; then
(
kill -9 $PID
)
fi

Answer 4

Here is another solution that may be useful for someone:
#!/bin/bash
kill-process-by-name(){
processes=$(ps -A)
kill -9 `echo "$processes" | grep "$1" | cut -f2 -d" "`
}
kill-process-by-name "start.sh"

Answer 5

trashPID=`pidof start.sh | awk '{print $1}'`
echo "$PID csshst will be stopped"
if [[ -z "$PID" ]]; then
(
kill -9 $PID
)
fi
purely