Intermediate Perl Learning Notes-chapter 4

exercise 2:

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

my @required = qw(sunscreen water_bottle slide_rule batteries radio);
my @gilligan = qw(red_shirt hat lucky_socks water_bottle);
my @skipper = qw(blue_shirt hat jacket preserver sunscreen);
my @professor = qw(sunscreen water_bottle slide_rule batteries radio);

my %all = (
"gilligan" => \@gilligan,
"skipper" => \@skipper,
"professor" => \@professor,
);

&check_items_for_all (\%all);

sub check_required_items
{
    my $who = shift;
    my $items = shift;
    my @missing = ();
    foreach my $item(@required)
    {
        unless (grep $item eq $_,@$items)
        {
            print "$who is missing $item.\n";
            push @missing,$item;
     }
    }
    if(@missing)
    {
        print "adding @missing to @$items for $who.\n";
        push @$items,@missing;
        }
}

sub check_items_for_all
{
    #####my $hr = shift;
    foreach my $person(sort keys %{$_[0]})
    {
        check_required_items $person,$_[0]->{$person};
    }
}

总结：

1.print提供列表环境,array和hash会自动展开成其元素列表相当于join($LIST_SEPARATOR,@array)or

join($",@array);

2.使用引用的一个最重要目的是:decoupling the code from the complex data structure on which it operates and reuse code