Prevent process from running when lock file exists.

with_lock.sh

#!/bin/bash

# filename   : with_local.sh
# created at : 2015-05-04 11:28:24
# author     : Jianing Yang <jianingy.yang@gmail.com>

if [ "$#" -lt 2 ]; then
    echo "Usage: $(basename $0) lockfile command"
    echo "Prevent process from running when lock file exists."
    echo
    echo "Example:"
    echo "  with_lock.sh sleep.lock sleep 10"
fi

lockfile="$1"
shift

# test lock
if ! ln -s "$$" "$lockfile" &>/dev/null; then
    pid="$(readlink $lockfile)"
    echo "another process (pid=$(readlink $lockfile)) is running."
    if [ ! -d "/proc/$pid" ]; then
        echo "this is a dangling lock file. i'll remove it"
        rm -f $lockfile
        # try again
        exec $0 $lockfile $@
    fi

    exit 111
fi

# run the program
$@

# remove lock
rm -f $lockfile