perl -MData::Dumper -e '%hash="foo"; print Dumper( \%hash )' # produces this... ( so far so good... ) # $VAR1 = { # 'foo' => undef # }; perl -MData::Dumper -e '%hash = undef; print Dumper( \%hash )' # produces: # $VAR1 = { # '' => undef # };