In case you need an example, this snippet shows the basics, you can easily test for

if (ref $_ eq 'ARRAY')

#!/usr/bin/perl

%CARD_DATA = (

    CARDS => {

        AX => {
            name       => "American Express",
            valid_card => "true",
            fee_code   => "1",
            currency   => {US=>'1',CA=>'2',GB=>'3'},
            misc_data  => [],
        },

        DI => {
            name       => "Diners Club",
            valid_card => "false",
            fee_code   => "",
            currency   => {US=>'1',CA=>'2',GB=>'3'},
            misc_data  => ["CVV=4"],
        },

        DS => {
            name       => "Discover",
            valid_card => "false",
            fee_code   => "",
            currency   => {US=>'1',CA=>'2',GB=>'3'},
            misc_data  => [],
        }
    }
);

my $depth = 0;
print_keys( \%CARD_DATA );

sub print_keys {
    my $href = shift;
    $depth++;
    foreach ( keys %$href ) {
        print '  ' x $depth, "--$_\n";
        print_keys( $href->{$_} ) if ref $href->{$_} eq 'HASH';
    }
    $depth--;
}
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