Here's a demo of a sub you might find useful. It descends the hash chain checking existence at each level. It returns [a reference to, to ensure logical truth] the value if everything exists. 
#!perl
use warnings;
use strict;

sub safe_exists {
    my ($href, @list_of_descent) = @_;
    use List::Util 'first';
    if (first {
            not (exists $href->{$_} and $href=$href->{$_})
        } @list_of_descent) {
        return ();
    }
    else {
        return \$href;
    }
}

my %hash = ('a' => {
                      'value' => 1,
                      'foo' => 'bar',
                   },
            'b' => {
                      'value' => 2,
                      'foo' => 'bar',
                   },
            'c' => {
                      'value' => 3,
                      'foo' => 'bar',
                   },
           );

for (qw(a b c d)) {
    if (my $href = safe_exists(\%hash, $_, 'value')) {
        print "$_ value is $$href\n";
    }
    else {
        print "Key $_ doesn't exist. Valid keys are: ";
        print join (", ", keys %hash), "\n";
    }
}

[download]
Caution: Contents may have been coded under pressure.

In reply to Re: Heisenberg Uncertainty Hash by Roy Johnson
in thread Heisenberg Uncertainty Hash by Sprad

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.