Your best solution is to do if ($hash{d} and !$hash{d}{value}) { ... }.

Instead of just checking the truth or otherwise of $hash{d}{value}, check for existence using the exists() function. That way you won't get weird bugs when the value is (eg) zero or the empty string. You might also want to check that $hash{d} is a reference to a hash before trying to access it.

Putting an exists there, (exists $hash{'d'}->{'value'}) still autovivificates $hash{'d'}. This might be surprising, but it is logical. After all, you are enquiring about the hash %{$hash{'d'}} (asking whether it contains the key 'd'). Since that hash doesn't exists yet, Perl does what it always does in that case: it creates it.

If you want to cover all your bases, and make sure no hash gets created as a side effect, be more explicite:

    if (exists $hash{'d'} && ref $hash{'d'} eq "HASH" && exists $hash{
+'d'}->{value}) { ... }
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The higher-level 'd' key is autovivified by checking for a lower-level key. Check existance of the higher-level key before doing anything with the lower level.

if (exists $hash{'d'} and !$hash{'d'}->{'value'}) {
    print "That key doesn't exist. Valid keys are: ";
    print join (", ", keys %hash);
}
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This is a well-known gotcha.

You've been bitten by auto-vivification. It means that since $hash{'d'} is undefined and you're asking it to be a hash reference, Perl creates an anonymous hash for you.

You probably want

# If record 'd' does not exist:
if (!$hash{'d'})
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Not as likely, but you might even want

# If record 'd' does not exist, or
# if record 'd' exists but has no field 'value':
if (!$hash{'d'} || !exists($hash{'d'}{'value'}))
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or

# If record 'd' does not exist,
# if record 'd' exists but has no field 'value', or
# if record 'd' exists and has field 'value' but is undefined:
if (!$hash{'d'} || !defined($hash{'d'}{'value'}))
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However, the equivalent to your code would be

# If record 'd' does not exist,
# if record 'd' exists but has no field 'value',
# if record 'd' exists and has field 'value' but is undefined,
# if record 'd' exists and has field 'value' but is 0,
# if record 'd' exists and has field 'value' but is "0", or
# if record 'd' exists and has field 'value' but is '':
if (!$hash{'d'} || !$hash{'d'}{'value'})
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Thanks for reducing the problem to a its minimum form.

Protocol demands it that I begin this by saying something like "sir, consider yourself bitten by AUTOVIVIFICATION". With that out of the way, here's a useful tutorial on the subject; also, here's a rant I wrote on this.

#!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";
    }
}
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