{
   my %h;
   1 if exists $h{key};
   print("exists:  ", (%h ? "auto-vivi" : "empty"), "\n");
}
{
   my %h;
   1 if defined $h{key};
   print("defined: ", (%h ? "auto-vivi" : "empty"), "\n");
}
{
   my %h;
   1 if $h{key};
   print("true:    ", (%h ? "auto-vivi" : "empty"), "\n");
}

__END__
exists:  empty
defined: empty
true:    empty