foreach my $i ($ref->%b} {
    print $i;           # I want to see the content of the hash.
}
[download]

"b" in the hash is now only a hash key, and therefore you cannot put a "%" sign before "b", but you need a %{...} to dereference the hash. This will work:

foreach my $i (  %{  $ref->{b}  }  ) {
    print $i;           # I want to see the content of the hash.
}
[download]

(It will print keys and values by turns.)