Another option you have is the built-in module File::Spec.

Here's a script that shows how you might use it. Things to note (details in the doco):

• $no_file - Set to a TRUE value, indicates these are paths to directories.
• grep { length } ... - Handles "... empty directory names ('') can be returned ...".
• with_trailing_slash - Extra test to show how trailing slashes are handled.

#!/usr/bin/env perl

use 5.010;
use strict;
use warnings;

use File::Spec;

my $no_file = 1;

while (my $path = <DATA>) {
    chomp $path;

    my ($volume, $directories, $file)
        = File::Spec->splitpath($path, $no_file);

    my @dirs = grep { length } File::Spec->splitdir($directories);

    my $last_dir = $dirs[-1];

    say qq{$path },
        q{.} x (24 - length($last_dir) - $path =~ m{\W$}),
        qq{ $last_dir};
}

__DATA__
y:/home/lib/directory/book
y:/home/lib/directory/book_manager
y:/home/lib/directory/piano_book
y:/home/lib/directory/with_trailing_slash/
[download]

Output:

$ pm_after_slash.pl
y:/home/lib/directory/book .................... book
y:/home/lib/directory/book_manager ............ book_manager
y:/home/lib/directory/piano_book .............. piano_book
y:/home/lib/directory/with_trailing_slash/ .... with_trailing_slash
[download]