Commonly, we use hashes for doing this sort of work, where you want to have a key (book ref) that holds information about the thing (the book's title). In this specific case, I've used a hash of hashes (HoH), and used regex capture groups (()) to grab the relevant parts of the regex to store. Here's a basic example. This assumes that the book's ref will always be in the same position (above the line containing the title, and any other items you want to store)

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

my %books;
my $book_ref;

while (<DATA>) {
    chomp;

    if (/^\s*book ref #(\d+)/i and $1){
        $book_ref = $1;
        $books{$book_ref} = {};
    }
    if (/^title\s+(.*)$/i and $1){
        $books{$book_ref}{Title} = $1;
    }
}

# print the whole shebang

for my $ref (keys %books){
    for my $book_element (keys $books{$ref}){
        print "Book ref: $ref, $book_element: $books{$ref}{$book_eleme
+nt}\n";
    }
}

# print one of the book's titles

print "$books{9969}{Title}\n";

__DATA__

Book ref #4346
Lent: Sun Jul 12 03:26:43 BST 2015
status Lent
Description: classic
title blah blah blah
last used: 2
color red
Pages 238
Publisher Bca
Type Hardback
Location: N/a
Author R jones

Book ref #9969
Lent: Sun Jul 12 03:26:43 BST 2015
status Lent
Description: classic
title My Little Pony
last used: 2
color red
Pages 238
Publisher Bca
Type Hardback
Location: N/a
Author R jones


__END__
Book ref: 4346, Title: blah blah blah
Book ref: 9969, Title: My Little Pony
My Little Pony
[download]

-stevieb