use strict;
use warnings;

my %hash1 = %{create()};
my $ref = create();
my %hash2; give(\%hash2);

print $hash1{'a'} . $ref->{'b'} . $hash2{'c'};

sub create {
    my %hash = ('a' => '1', 'b' => '2');
    return \%hash;
}

sub give {
    my $ref = shift;
    %$ref = ('c' => '3', 'd' => '4');
}
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Here's three ways to pass hash data from a sub.