Your answer is here. Just look for the (second) listed type of variable, arrays.

Here is the bit you want to see (about arrays in scalar context).

You might be tempted to use $#array + 1 to tell you how many items there are in an array. Don't bother. As it happens, using @array where Perl expects to find a scalar value ("in scalar context") will give you the number of elements in the array: 1. if (@animals < 5) { ... }

Here is your program using those features.

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

# the program
my %hash = (
        'one' => [1],
        'two' => [2,2],
        'three' => [3,3,3],
);

print "$hash{one}[0]\n";
print "$hash{two}[0]\n";
print "$hash{three}[0]\n";

while (my ($key, $aref) = each %hash) {
    # dereference array_reference
    # (and the @$aref array is in scalar context)
    printf "key=%s size=%d\n", $key, @$aref;
}
[download]

Prints:

1
2
3
key=three size=3
key=one size=1
key=two size=2
[download]