dir structure looks like

...
lib/B.pm
...
lib/C/C1.pm
...
[download]

lib/B.pm

As previously stated, B.pm will already exist on your system. Attempting to write new code with "package B;" will cause you all sorts of problems. You should avoid this name.

lib/C/C1.pm

That's fine. The class name will become "C::C1". My previously posted "lib/C1.pm" should be moved to "lib/C/C1.pm", and the first line should be changed to:

package C::C1;
[download]

In my "./acd.pl", you should change

use C1;

my $c1 = C1::->new();
[download]

to

use C::C1;

my $c1 = C::C1::->new();
[download]

After making those changes, note the difference in the last line:

$ ./acd.pl
A=HASH(0x9897d0)
A-bar
D=HASH(0x989890)
D-bar
whos_who() is in package: C
$self is in package: C::C1
[download]

The hexadecimal values in "X=HASH(0xhhhhhh)" will likely be different: that's not significant; you could get different values on separate runs using the same code.