You've created $a{bar} by your second check, just as perldoc -f exists explains.

Although the deepest nested array or hash will not spring into existence just because its existence was tested, any intervening ones will. Thus "$ref->{"A"}" and "$ref->{"A"}->{"B"}" will spring into existence due to the existence test for the $key element above. This happens anywhere the arrow operator is used, including even:...

In reply to Re: Re2: Check for existence in a hash of hashes by Fletch
in thread Check for existance in a hash of hashes by Perl_User

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