Simple, general pid lock file mechanism for ksh, for cron jobs (esp. on Solaris)

cron_runner

#!/bin/ksh

function grab_lock {
    pid_lock $lockfile || exit 1

    if [ ! -e $lockfile ]; then
        print -u 2 "Lock file $lockfile should exist!"
        exit 1
    fi
}

function run_program {
    if [ -e $HOME/.profile ]; then
        . $HOME/.profile
    fi

    print -u 2 "$$: executing: $run_cmd"
    exec $run_cmd
}

function release_lock {
    print -u 2 "$$: completed, releasing lock."
    rm $lockfile
}

. `dirname $0`/lock.ksh
basedir=`dirname $0`/../..

config=$1
if [ "$config" == "" ]; then
    print -u 2 "Usage: $0 <config>"
    exit 2
fi

if [ ! -e "$config" ]; then
    print -u 2 "Error: config file $config does not exist!"
    exit 2
fi

# read the config file
. $config

## check settings
if ! (test "$lockfile" && test "$logfile" && test "$run_cmd"); then
    print -u 2 "Error: config file $config must specify lockfile, logfile, and run_cmd!"
    exit 2
fi

redirect 2>>$logfile

grab_lock
(run_program)
release_lock

lock.ksh

function pid_lock {
    typeset lockfile
    lockfile=$1
    
    if [ -e $lockfile ]; then
        lock_pid=`cat $lockfile`
        if kill -0 $lock_pid 2>/dev/null; then
            # still running
            print -u 2 "$$: PID $lock_pid still running, exiting!"
            return 1
        else
            # stale lock
            print -u 2 "$$: Stale lock from PID $lock_pid, taking lock."
        fi
    fi

    if print "$$" > $lockfile; then
        return 0
    else
        print -u 2 "$$: Failed to write lock file $lockfile!"
        return 1
    fi
}