@{ $netifaces->{ $_ } }{ @nets } = (1) x @nets for @eths;
   ^^^^^^^^^^ a hash reference

@{ $netifaces->{ $_ } }{ @nets } = (1) x @nets for @eths;
   ^^^^^^^^^^^^^^^^^^ an element in that hash

@{ $netifaces->{ $_ } }{ @nets } = (1) x @nets for @eths;
                                   iterated over ^^^                                              

@{ $netifaces->{ $_ } }{ @nets } = (1) x @nets for @eths;
                                      by these keys ^^^^^

@{ ... }{ @nets }
^^^^^^^^^^^^^^^^^^ a hash slice with the keys in @nets

@{ ... }{ @nets } = (1) x @nets ...;
       is assigned ^ ^^^^^^^^^^^ a list of '1's the size of @nets