You're going to have three loops no matter what. You seem to be asking how to hide them. That's what subs are for. 
sub extract {
   my ($rez) = @_;
   my @flattened;
   for my $host ( keys %$rez ) {
   for my $tgt  ( keys %{ $rez->{$host}{tgt} } ) {
   for my $dev  ( keys %{ $rez->{$host}{tgt}{$tgt} } ) {
      push @rv, [ $tgt, $dev, $rez->{$host}{tgt}{$tgt}{$dev} ];
   }}}
   return @flattened;
}

for (extract(\%rez)) {
    my ($tgt, $dev, $val) = @$_;
    ...
}

[download]
Or a callback approach: 
sub walk(&@) {
   my ($cb, $rez) = @_;
   for my $host ( keys %$rez ) {
   for my $tgt  ( keys %{ $rez->{$host}{tgt} } ) {
   for my $dev  ( keys %{ $rez->{$host}{tgt}{$tgt} } ) {
      $cb->($tgt, $dev, $rez->{$host}{tgt}{$tgt}{$dev});
   }}}
}

walk {
    my ($tgt, $dev, $val) = @_;
    ...
} \%rez;

[download]

In reply to Re: A better way for walking through HoHoH ? by ikegami
in thread A better way for walking through HoHoH ? by ZlR

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.