thank you for the snippet, I really appreciate it.
I found the need of handling arrays too: append them if found.
to combine {a:[1,2]} and {a:[3,4]} into {a:[1,2,3,4]} I had to edit the while loop in the middle: 
   while (my ($k,$v) = each %merged) {                                                      
     my @hashes = grep { ref $_ eq 'HASH' } @$v;
     #$merged{$k} = $v->[0] if (@$v == 1 && !ref $v->[0]);

     # append text separated with \n\n, but do not duplicate identical values
     $merged{$k} = join "\n\n", do { my %seen; grep {!$seen{$_}++} @$v} if (!ref $v->[0]);

     # append arrays one to other
     @{$merged{$k}} = map {@$_} @$v if (ref $v->[0] eq 'ARRAY');

     $merged{$k}  = mergehashes(@hashes) if @hashes;
   }
I thought someone else will find this useful too.

In reply to Re: Merge Multiple Hashes by Anonymous Monk
in thread Merge Multiple Hashes by shotgunefx

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.