How can I check if a key exists in a deep Perl hash?

Question

If I understand correctly, calling if (exists $ref->{A}->{B}->{$key}) { ... } will spring into existence $ref->{A} and $ref->

Answer 1

Check every level for existence before looking at the top level.

if (exists $ref->{A} and exists $ref->{A}{B} and exists $ref->{A}{B}{$key}) {
}

If you find that annoying you could always look on CPAN. For instance, there is Hash::NoVivify.