Hash in Perl adds key if it does not exist

Question

I have the following perl script which is storing some details in a hash. After populating some entries in the hash, I\'m printing the content of the hash which produces the fol

Answer 1

This is called autovivification. It is a feature of Perl that allows you to use a hash element that you haven't previously declared or initialized. It occurs whenever an undefined value (like $components{'11:Name11'}) is dereferenced (which happens when Perl tries to evaluate $components{'11:Name11'}{'name'}).

There is a autovivification pragma that you can unuse to disable this behavior.

{
    no autovivification;
    if ($hash{"non-existent-key"}{"foo"}) {  # won't create $hash{"non-existent-key"}
    ...
}