use Linux::Inotify2;

my $target = '/home/tart';
my $in2 = Linux::Inotify2->new();
die "Inotify2: $!" if (! defined $in2 );

$in2->watch ($target, IN_CLOSE_WRITE, \&translate_event) or 
    die "watch: $!";
   
$in2->poll while 1;    # blocking call

# User written callback
sub translate_event
{
   my ($ev) = @_;
   if ($ev->fullname eq 'config.cfg') {
       # File was written to (and closed), so run the script
       system(script.pl);  # or whatever
       if ($?) {
           # Oops, it failed
       }
    }
}
[download]

And unless you have a file system that allows you to have hooks on modifications, the answer is that there are no ways.

The closest thing I can think of would be to run your script (or a wrapper) as a cron job (Unix/Linux)or a scheduled task (Windows) and have it take whatever action you want if conditions are met (i.e. if a file has been modified in the last hour or whatever you would look for).

Not instant, but you can have it run fairly frequently. Might work for you, depending on exactly what your application is.