Here are a two possible ways to find which keys appear in multiple hashes. Neither of these will report how many occurrences, or which hash they appear in - but either would be fairly easy to add.

use strict;
use warnings;
my %hash1 = (a => 1, b => 2);
my %hash2 = (a => 1, c => 3);
my %hash3 = (d => 1, c => 3);

# Method 1
# Create a hash for tallying the number of times keys occur in the oth
+er hashes.
my %key_bucket = ();
for my $key (keys %hash1, keys %hash2, keys %hash3) {
  $key_bucket{$key}++;
}
my @duplicates = grep {$key_bucket{$_} > 1} keys %key_bucket;

print "Method 1:\n";
print "$_\n" for @duplicates;


# Method 2
# Create a list of unique keys, then check how many hashes each key ap
+pears in
print "Method 2:\n";
my %unique = map {$_ => 1} keys %hash1, keys %hash2, keys %hash3;
for my $key (keys %unique) {
    my (@matches) = grep {exists $_->{$key}} \%hash1, \%hash2, \%hash3
+;
    print "$key\n" if @matches > 1;
}
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