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DiBona Don't ask to ask, just ask   by gods on Aug 24, 1999 at
22:42 UTC ( #253=perlfunc: print w/ replies, xml ) Need Help??
See the current Perl documentation for exists.   exists - test
whether a hash key is present  exists EXPR  Returns TRUE if the
specified hash key exists in its hash array, even if the
corresponding value is undefined.      print "Exists\n" if
exists $array{$key};     print "Defined\n" if defined
$array{$key};     print "True\n" if $array{$key};  A hash
element can be TRUE only if it's defined, and defined if it
exists, but the reverse doesn't necessarily hold true.  Note
that the EXPR can be arbitrarily complicated as long as the
final operation is a hash key lookup:      if (exists
$ref->{"A"}{"B"}{$key}) { ... }  Although the last element will
not spring into existence just because its existence was tested,
intervening ones will. Thus $ref->{"A"} $ref->{"B"} will spring
into existence due to the existence test for a $ke