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
$key
element. This autovivification may be fixed in a later
release.
If rather than formatting bugs, you encounter substantive content errors in these documents, such as mistakes in the explanations or code, please use the perlbug utility included with the Perl distribution.