while ( defined( my $record = <$input_fh> ) ) {
    my %record_hash = rec2hash( $record );
    while ( my ( $field, $value ) = each %record_hash ) {
        my $variant = variant_of( $value );
        $variants_in{ $record }{ $field }{ $variant } = 1;
        push @{ $records_for{ $field }{ $variant } }, $record;
    }
}