my %hash = ( 'key' => 'value' );
print "exists \$hash{'key'}\n" if exists $hash{'key'};
my @array = ( 'value' );
print "exists \$array[\$index]\n" if exists $array[0];
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exists operator argument is not a HASH element at test-5.00503.perl line 7.
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exists $hash{'key'}
exists $array[$index]