...
  my $path = File::Spec->catdir($self->{mnt}, @path);
  ...

  # and

  $self->add_song(glob(File::Spec->catpath($self->{mnt}, "iPod_Control", "Music", "*", "*")));

##</code><code>##

   my $dir = $self->storage_dir;
   ...
   my @files = map {
            scalar( s/\.$extension//, basename $_)
        } glob("$dir/*.$extension");

##</code><code>##

...
foreach my $dir ( @ARGV ) {
  unless ( -d $dir ) {
    warn("$dir: not a directory -- skipped\n");
    next;
  }
  ...

  my @files = sort map { $1 if /([^\/]+)\.mp3$/ } glob("$dir/[0-9]*.mp3");