How to stop a shell script correctly?

Question

I've written a small bash script to start a program every 3 seconds. This script is executed on startup and it saves its PID into a pidfile:

#!/bin/bash

echo $$ > /var/run/start_gps-read.pid

while [ true ] ; do
    if [ "$1" == "stop" ] ;
    then
        echo "Stopping GPS read script ..."
        sudo pkill -F /var/run/start_gps-read.pid
        exit
    fi
    sudo /home/dh/gps_read.exe /dev/ttyACM0 /home/dh/gps_files/gpsMaus_1.xml
    sleep 3
done

The problem is, I can't terminate the shell script by calling start_gps-read.sh stop. There it should read the pidfile and stop the inital process (from startup).

But when I call stop, the script still runs:

dh@Raspi_DataHarvest:~$ sudo /etc/init.d/start_gps-read.sh stop
Stopping GPS read script ...

dh@Raspi_DataHarvest:~$ ps aux | grep start
root       488  0.0  0.3   5080  2892 ?        Ss   13:30   0:00 /bin/bash /etc/init.d/start_gps-read.sh start
dh        1125  0.0  0.2   4296  2016 pts/0    S+   13:34   0:00 grep start

Note: The script is always executed as sudo.

Does anyone know how to stop my shell script?

Answer 1

The "stop" check needs to come before you overwrite the pid file, and certainly doesn't need to be inside the loop.

if [ "$1" = stop ]; then
    echo "Stopping ..."
    sudo pkill -F /var/run/start_gps-read.pid
    exit
fi

echo "$$" > /var/run/start_gps-read.pid
while true; do
    sudo /home/dh/gps_read.exe ...
    sleep 3
done