How to incorporate hash inside hash in perl? - perl

Question

my %book = (
'name' => 'abc',
'author' => 'monk',
'isbn' => '123-890',
'issn' => '#issn',
);
my %chapter = (
'title' => 'xyz',
'page' => '90',
);
How do I incorporate %book inside %chapter through reference so that when I write "$chapter{name}", it should print 'abc'?

Answer 1

You can copy the keys/values of the %book into the %chapter:
#chapter{keys %book} = values %book;
Or something like
%chapter = (%chapter, %book);
Now you can say $chapter{name}, but changes in %book are not reflected in %chapter.
You can include the %book via reference:
$chapter{book} = \%book;
Now you could say $chapter{book}{name}, and changes do get reflected.
To have an interface that allows you to say $chapter{name} and that does reflect changes, some advanced techniques would have to be used (this is fairly trivial with tie magic), but don't go there unless you really have to.

Answer 2

You could write a subroutine to check a list of hashes for a key. This program demonstrates:
use strict;
use warnings;
my %book = (
name => 'abc',
author => 'monk',
isbn => '123-890',
issn => '#issn',
);
my %chapter = (
title => 'xyz',
page => '90',
);
for my $key (qw/ name title bogus / ) {
print '>> ', access_hash($key, \%book, \%chapter), "\n";
}
sub access_hash {
my $key = shift;
for my $hash (#_) {
return $hash->{$key} if exists $hash->{$key};
}
undef;
}
output
Use of uninitialized value in print at E:\Perl\source\ht.pl line 17.
>> abc
>> xyz
>>