I now need to request an exclusive lock on that file. If granted, I know that no other instance of this program is running and I can continue. Now I need to read this file, it contains the exit status of the last instance of this program. This lets me know where I need to start up at (I maintain a state file).

After this file is read and I know where to begin in my processing I wish to truncate this file and add the information from this instance of the program. Can I just reopen the file like this open(FH,">./program.pid");? Will this just replace the previous instance of 'FH' or will I be stacking things up?

Also a concern, when I reopen the file with the same filehandle, it is (I think) essentially closing the previous one. This would make me lose my exclusive lock on the file. I could immediately place an exclusive lock again, but this could end up an a race state with another version of this program.

Here's a little example of what I want to do:

...

open(PIDFILE,">>$pidFile") or die
     "Cannot open pidfile, $pidFile: $!\n";

if (! &lock(*PIDFILE) )
{
    print "\n\tCannot obtain exclusive lock on $pidFile\n",
          "\tThere must be another instance of this\n",
          "\tprogram running.  Exiting.\n\n";
    exit;
}

# GOT LOCK
my @arr = (<PIDFILE>);
open(PIDFILE,">$pidFile");

print PIDFILE "$$\n";

...
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