This version is slightly more compact by using map to navigate through the tree. A wrong path will return undef. I use the grep because so you can add empty "/" at the beginning or end of the filename, at your will.

use Data::Dumper;

$VAR1 = {
  'misc' => {},
  'docs' => {
    'howtos' => {
      'email' => {
        'index.html' => {
          'date' => '21-1-2004',
          'size' => '691'
        }
      },
      'ftp' => {},
      'ssh' => {}
    }
  }
};

$fs = "/docs/howtos/email/";
$v = $VAR1;

# this is the actual processing
map { $v = $v->{$_} } grep { length > 0 } split m./., $fs ;

print Dumper $v;
[download]

Enjoy!

Note. I have been reading Paul Graham's On Lisp lately, does it show? :)

Note: I submitted this comment before seeing's BrowserUk's, looks like we had the same idea.