Section A.3. Answers for Chapter 4

A.3. Answers for Chapter 4

A.3.1. Exercise 1

They're all referring to the same thing, except for the second one, ${$ginger[2]}[1]. That one is the same as $ginger[2][1], whose base is the array @ginger, rather than the scalar $ginger.

A.3.2. Exercise 2

First, we construct the hash structure:

 my @gilligan = qw(red_shirt hat lucky_socks water_bottle); my @professor = qw(sunscreen water_bottle slide_rule batteries radio); my @skipper = qw(blue_shirt hat jacket preserver sunscreen); my %all = (   "Gilligan" => \@gilligan,   "Skipper" => \@skipper,   "Professor" => \@professor, ); 

Then we pass it to the first subroutine:

 check_items_for_all(\%all); 

In the subroutine, the first parameter is a hashref, so we dereference it to get the keys and the corresponding values:

 sub check_items_for_all {   my $all = shift;   for my $person (sort keys %$all) {     check_required_items($person, $all->{$person});   } } 

From there, we call the original subroutine:

 sub check_required_items {   my $who = shift;   my $items = shift;   my @required = qw(preserver sunscreen water_bottle jacket);   my @missing = (  );   for my $item (@required) {     unless (grep $item eq $_, @$items) { # not found in list?       print "$who is missing $item.\n";       push @missing, $item;     }   }   if (@missing) {     print "Adding @missing to @$items for $who.\n";     push @$items, @missing;   } }