friends.pl

use strict;
use warnings;
use Data::Dumper;

my %people = (
    cody => {
        friends => ['aaron', 'alyx', 'foo', 'cow']
    },
    aaron => {
        friends => ['alyx', 'cody', 'foo', 'bar', 'moo', 'cow']
    }
);

sub find_mutual
{
    my @person = @_;
    my @mutual;
    foreach my $friend (@{ $people{$person[0]}{friends} })
    {
        if ($friend ~~ @{ $people{$person[1]}{friends} })
        {
            push @mutual, $friend;
        }
    }
    return @mutual;
}

my @mutual_friends = find_mutual('cody', 'aaron');
printf("Your mutual friends: %s\n", join(", ", @mutual_friends));