A Bash Process Controller to Start, Stop and Restart an Daemon Program

$ sudo service mysql stop
$ sudo service mysql start
$ sudo service mysql restart

#!/bin/bash
 
# Function: to start, stop and restart the application.
# Usage: $0 start|stop|restart application
 
if [[ "$#" -lt 2 ]]; then
    echo "Usage: $0 start|stop|restart command"
    echo "$# parameters given."
    exit 1
fi
 
PID_FILE_PATH="runner.pid"
 
case "${1}" in
    start)
        # Already running
        if [ -f ${PID_FILE_PATH} ]; then
            pid=$(cat ${PID_FILE_PATH})
            if $(ps -p ${pid} > /dev/null); then
                echo "Already running [PID: ${pid}], you can stop it and retry."
                exit 1
            fi
        fi
 
        nohup "$2" 2>&1 \
            & echo $! > ${PID_FILE_PATH}
 
        if [ $? -eq 0 ]; then
            echo "Succeeded to start $2."
        else
            echo "Failed to start $2."
            exit 1
        fi
    ;;
    stop)
        kill $(cat ${PID_FILE_PATH})
 
        if [ $? -eq 0 ]; then
            rm ${PID_FILE_PATH}
            echo "Succeeded to stop $2."
        else
            echo "Failed to stop $2."
            exit 1
        fi
    ;;
    restart)
        ${0} stop "$2" && sleep 1 && ${0} start "$2"
    ;;
esac

$ ./runner.sh stop yes
cat: runner.pid: No such file or directory
kill: usage: kill [-s sigspec | -n signum | -sigspec] pid | jobspec ... or kill -l [sigspec]
Failed to stop yes.
$ ./runner.sh start yes
Succeeded to start yes.
nohup: appending output to 'nohup.out'
$ ./runner.sh restart yes
Succeeded to stop yes.
Succeeded to start yes.
nohup: appending output to 'nohup.out'
$./runner.sh stop yes
Succeeded to stop yes
.