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This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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4.63: Why don't my tied hashes make the defined/exists distinction?

This depends on the tied hash's implementation of EXISTS(). For example,
there isn't the concept of undef with hashes that are tied to DBM*
files. It also means that exists() and defined() do the same thing with
a DBM* file, and what they end up doing is not what they do with
ordinary hashes.



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