Shell Programming and Scripting

# This is to examine whether the lockfile existed
[ -f "${0}.lock" ] && exit -1
# Create the lock file
lockfile ${0}.lock
sleep 40
# Release the lock file manually
rm -f ${0}.lock

# This is to examine whether the lockfile existed
[ -f "${0}.lock" ] && exit -1
# Create the lock file
lockfile ${0}.lock
sleep 40
# Release the lock file manually
rm -f ${0}.lock

lockfile /tmp/lock; sleep 10; rm -f /tmp/lock

lockfile /tmp/lock && echo "Finaly, I'am running..."; rm -f /tmp/lock

lockfile -r0 /tmp/lock && echo "Finaly, I'am running..."; rm -f /tmp/lock

# Create the lock file
lockfile -r0 ${0}.lock && {
     # Your code goes here!
}
# Release the lock file manually
rm -f ${0}.lock

lock_on()
{
    local f=$1
    local freefd=6  ## do not use fd 5

    ## make sure the file be there
    mkdir -p "$( dirname $f )"
    touch "$f"

    ## find a free fd
    while (( freefd <= 9 )); do
        [[ -L /dev/fd/$freefd ]] || break
        (( freefd++ ))
    done

    (( freefd == 10 )) && return 1

    ## open the lock file
    eval "exec $freefd< \"$f\""
}

is_locked()
{
    local f=$1

    fuser "$f" &> /dev/null
}

lock="/tmp/.$( basename $0 ).lock"
is_locked "$lock" && exit 1
lock_on "$lock"
## do something here