use reference to modify the orignal array

#!/usr/bin/perl -w
#
use strict;

my @skipper = qw(blue_shirt hat jacket preserver sunscreen);
check_required_items('The Skipper', \@skipper);
print "@skipper\n";
sub check_required_items{
    my $who = shift;
    my $items = shift;
    my @required = qw(preserver sunscreen water_bottle jacket);
    my @missing=();

    foreach my $item (@required){
        unless( grep $item eq $_, @$items){
            print "$who missing $item\n";
            push @missing, $item;
        }
    }
    if (@missing){
        push @$items, @missing;
    }
}

#The Skipper missing water_bottle
#blue_shirt hat jacket preserver sunscreen water_bottle

here we insert the missing items to the orignal array. if dont use the reference, the change will be not affected the orignal array.