#!/usr/bin/perl

use warnings;
use strict;

$|++;

use Linux::Inotify2;

        my $this1 = new Linux::Inotify2
                or die "unable to create new inotify object: $!";
        $this1->watch ("/tmp/a12", IN_MODIFY, sub {
          my $e = shift;
          print "\nin watch - $e = \n";

        });

$this1->poll;


If I run this and there is a file /tmp/a12, on ubuntu 18.4 I get the event
if I then: touch -m /tmp/a12.  On ubuntu 16.4 I do not.