Check if the process is running and if it is already running

Question

I have a shell script with methods:

start(){
echo "Hello world"
}

stop(){
ps -ef|grep script.sh|grep -v grep|xargs kill
}

while [ "$1" != "" ]; do
case "$1" in
        start)
            start
            ;;
        stop)
            stop
            ;;
        *)
            echo $"Usage: $0 {start|stop}"
            exit 1
        esac
   shift
done

I run this script with this command: ./script.sh startto call the start.Now method, I want to check if this process is running and if it is already completed. I tried some solutions on the Internet but nothing worked. Someone please help. The solutions I tried were:

if [ -f /var/tmp/script.lock ]; then
  echo "Already running. Exiting."
  exit 1
else
  touch /var/tmp/script.lock
fi
<main script code>
#some code
rm /var/tmp/script.lock

Other:

PID=$(ps -ef | grep script.sh|grep -v grep)

   if [ -z $PID ]; then
       echo "Process already running"
       exit   
fi

These solutions do not work and do not exit, even when the process is just beginning.

Answer 1

.lock . - - script . , PID , PID.

if [ -f /var/tmp/script.lock ] && kill -0 $(cat /var/tmp/script.lock); then
  echo "Already running. Exiting."
  exit 1
else
  echo $$ > /var/tmp/script.lock
fi
<main script code>
#some code
rm /var/tmp/script.lock

kill -0 , , : PID ( root, , ).

- , , script, PID . PID , , , .

, script , , . , lockfile , .

Answer 2

script.

#!/bin/bash
export JAVA_HOME=/usr/java/jdk1.7.0_25

checkpid()
{
        echo $(ps -ef | grep "LiquidityWarning.jar" | grep -v grep | awk '{ print $2}')
}

start ()
{
    if [ $(checkpid) ] ; then
        echo -e "\n$(date +%Y%m%d-%H:%M:%S) LiquidityWarning.jar is running (pid:$(checkpid))\n"
    else
        echo ""
        printf "$(date +%Y%m%d-%H:%M:%S) LiquidityWarning.jar is starting..."
        cd /app/mservice/CBTK_new
        /usr/java/jdk1.7.0_25/bin/java -jar LiquidityWarning.jar > /dev/null 2>&1 &

    fi

}

stop ()
{
    if [ $(checkpid) ] ; then
        kill -9 $(checkpid)
        echo -e "\n$(date +%Y%m%d-%H:%M:%S) LiquidityWarning.jar stop success\n"
    fi

}

status ()
{
        if [ $(checkpid) ] ; then
        echo -e "\n$(date +%Y%m%d-%H:%M:%S) LiquidityWarning.jar is running (pid:$(checkpid))\n"
    else    
        echo -e "\n$(date +%Y%m%d-%H:%M:%S) LiquidityWarning.jar is not started\n"
    fi
}

restart()
{
        if [ $(checkpid) ] ; then
                stop
                sleep 2
                start
        else
                echo -e "\n$(date +%Y%m%d-%H:%M:%S) LiquidityWarning.jar is not started\n"
        fi
}

case "$1" in
  start)
      start
      ;;
  stop)
      stop
      ;;
  restart)
      restart
      ;;
  status)
      status
      ;;
  *)
    echo -e "\nUsage: $0 {start|stop|status|restart|reload}\n"
      exit 1
      ;;
esac