but this is NOT working.

It's always a good idea to mention how exactly it doesn't work — that way you enhance your chances of getting a useful reply, because not everyone is willing to install non-standard modules (+ dependencies) just to figure out what you could have mentioned right away. And often, an educated guess can be made without having the module installed, as long you have all relevant info available.  But thanks for following up with self-contained sample code.

That said, I did install the module to confirm my suspicion that the not-working output is 

The Simpsons
`- name = Homer

[download]

Reason is that if you only let 'name' pass through the filter, DumpTree won't recurse into the other entries 'kids' and 'wife'... In other words, in this particular case, you could do: 

return('HASH', undef, grep { !/^surname$/} keys %$s) ;

[download]

Output: 

The Simpsons
|- wife 
|  `- name = Marge 
|- name = Homer 
`- kids 
   |- 0 
   |  `- name = Bart 
   |- 1 
   |  `- name = Lisa 
   `- 2 
      `- name = Maggie

[download]

In reply to Re^3: Help to understand the Data::TreeDumper Filters by Eliya
in thread Help to understand the Data::TreeDumper Filters by Dirk80

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.