$ perl -
warn \my %hash;
warn \my(%hash);
^Z
HASH(0x99aa14) at - line 1.
Warning: something's wrong at - line 2.

$ perl -MO=Deparse -
warn \my %hash;
warn \my(%hash);
^Z
warn \my(%hash);
warn \(my(%hash));
- syntax OK


##</code><code>##

$ perl -le " warn scalar(\my %hash)"
HASH(0x99aa34) at -e line 1.

$ perl -le " warn scalar(\my(%hash))"
SCALAR(0x3f4788) at -e line 1.

$ perl -MData::Dump -le " dd scalar(\my(%hash))"
\undef