[Shell-Script] create a lock system for your code

Here is the code for making a lock system in your shell-script program.
The main utility of the lock system is to be sure to not running your code while another process of the same code is running.

The main principe is to create a lock file when the code is running, and check the existance of this file each time you're launching it.

NB : the variable $exec is the name of the script you want to execute.

#-- Parameters:
exec="./my-script.sh"
NAME="my-script"
LOCK="/tmp/${NAME}.lock"
out="/tmp/${NAME}-$(/bin/date '+%Y%m%d').out"

#-- Error Function:
error () {
echo "$1" 1>&2
exit 1
}

#-------------------------
# Launch the code
#-------------------------
if [ -f "$LOCK" ]
 then
   if [ "$(ps -p `cat $LOCK` | wc -l)" -gt 1 ]; then
   #-- process is still running
    echo "Quit at start: lingering process `cat $LOCK`"
        error "Daemon already running (not launched)!"
        exit 10
   else
   #-- process not running, but lock file not deleted
     echo "process not running, but lock file not deleted"
   rm $LOCK
  echo $$ >> "$LOCK"
 fi
else
  echo "create lock"
  echo $$ >> "$LOCK"
  echo "done (pid=$$)"
  # launch the code:
  ksh ${exec} >> $out 2>&1

fi

rm $LOCK