# Why initialise a scalar to an empty list?
our $HSH2 :shared = (); 

# Assign a ref to an anonymous hash
$HSH2 = {};             

# Assign a ref to another anon. hash to a new element of the first.
$HSH2->{123} = {};      

# Assign a string to an element of the second.
$HSH2->{123}->{456} = 'foo.xml';