• Take action if a inner key exists as an inner key in another hash.
• Know which value came from which hash/key
• Take default action if no match

#!/usr/bin/perl
use strict;
use warnings;

my %hash1 = (
    foo => { 'a' => 1, 'b' => 2, 'c' => 3 },
    bar => { 'd' => 1, 'e' => 2, 'f' => 3 },
);

my %hash2 = (
    blah => { 'm' => 1, 'd' => 2, 'a' => 3 },
    asdf => { 'z' => 1, 'l' => 2, 'b' => 3 },
);

for my $outer_key ( keys %hash1 ) {
    for my $inner_key ( keys %{ $hash1{$outer_key} } ) {
        my ($h2_outer, $h2_inner) = Find_Key( $inner_key , \%hash2 );
        if ( $h2_inner ) {
            # do something : $outer_key, $inner_key, $h2_outer, and $h
+2_inner
        }
        else {
            # do your other thing
        }
    }
}

sub Find_Key {
    my ($match, $hash) = @_;
    for my $key ( keys %$hash ) {
        for ( keys %{ $hash->{$key} } ) {
            return ($key, $_) if $_ eq $match;
        }
    }
    return (undef, undef);
}
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Cheers - L~R

Thank you L~R
This code was much clear to me, only one question should I also return the value of the $h2_inner(key) in the sub?

Anonymous Monk,
That is a matter of personal choice.

The values can be looked up once the keys are known regardless of where in the code you are.

There are also ways to make optimizations to this code that might make it less clear what is going on. When trying to understand something that seems complex it is often beneficial to work with a foundation that you fully understand and then add the complexity piece by piece.

Cheers - L~R