my $book_regex = qr/^Book ref #(\d+)/; # (\d+) will capture the ref into $1
my ($ref, $title, ...);
while (<DATA>) {
    # you may need to chomp the lines
    $ref = $1 if /$book_regex/;
    $title = $1 if /^title\s+(.*)/;
    # other regexes for title, etc.
}
# now you can use $ref and $title