Thanks for the suggestions, the problem is that when you get the event that the file has moved the copy does not yet exist (preventing a new watch), so you need to watch the directory as well...

Here what seems to work for me, any improvements welcome:

 
use strict;

use Linux::Inotify2;
use File::Basename qw(dirname);
use File::Spec;

$|++;

my ($file_to_watch)=@ARGV;

my $notify = Linux::Inotify2->new or die $!;

&setup_watch;

sub setup_watch {
  $notify->watch ($file_to_watch, IN_MODIFY | IN_MOVE_SELF, \&watch_fi
+le) or die $!;
}

sub watch_file {
  my($e)=@_;

  my $fn = $e->fullname;

  if($e->IN_MODIFY) {
     print "$fn changed\n";
  }

  if($e->IN_MOVE_SELF) {
     print "old $fn moved\n";
     $e->w->cancel;
     my $dir = dirname $fn;
     $notify->watch ($dir, IN_CREATE, \&watch_dir) or die $!;
  }
}

sub watch_dir {
  my($e)=@_;
  
   my $fn = File::Spec->canonpath($e->fullname);
   return unless $fn eq $file_to_watch;

   $e->w->cancel;
   print "$fn newly created (probably changed)\n";
   setup_watch;
}

while(1) { 
  my $n = $notify->poll; 
  print "handled $n events\n\n"; 
}
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