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%hash = ( 
    name  => 'Rhesa',
...
    dog   => 'Spot',
    cat   => 'Stofje',
);

%pets = (
    dog   => 'Spot',
    cat   => 'Stofje',
);

%pets = (
    dog => $hash{dog},
    cat => $hash{cat},
);

my @animals = qw( dog cat );
my %pets;
@pets{ @animals } = @hash{ @animals };

%pets = map { $_ => $hash{$_} }
        qw( dog cat );

sub hash_slice {
    my ($hr, @k) = @_;
...

# use like this:
%pets = hash_slice( \%hash, qw( dog cat ) );

@headers = qw(
    firstname lastname
...
    title bookcode isbn
    quantity
);

# %orderline comes from the csv
my $customer = Customer->find_or_create({
    firstname => $orderline{firstname},
    lastname  => $orderline{lastname},
});