Shell Only process

#!/bin/bash


LOCKFILE=/tmp/lock.txt
OnlyProcess() {


#The signals listed below may be available for use with kill.
#When known constant, numbers and default behavior are shown.
#Name Num Action Description
#0 0 n/a exit code indicates if a signal may be sent
        if [ -e ${LOCKFILE} ] && kill -0 `cat ${LOCKFILE}`; then
                echo "already running"
                exit
        fi


        # make sure the lockfile is removed when we exit and then claim it
        trap "rm -f ${LOCKFILE}; exit" INT TERM EXIT
        echo $$ > ${LOCKFILE}
}


OnlyProcess
sleep 1000