Neat solution...but when using 'B', it produces numbers greater than 6-bits can hold:

P:\test>perl
print join'|',
     unpack "C*",    # 16 6-bit numeric values
     pack   "B6"x16, # string of 16 bytes, each  holding a 6-bit value
     unpack "a6"x16, # 16 6-character base-2  strings
     unpack "B*",    # 96-character base-2  string
     "twelve bytes"; # 12-byte packed string
^Z
116|28|116|148|108|28|100|148|32|24|36|228|116|24|84|204
[download]

Switching to 'b' fixes that:

P:\test>perl
print join'|',
     unpack "C*",    # 16 6-bit numeric values
     pack   "b6"x16, # string of 16 bytes, each  holding a 6-bit value
     unpack "a6"x16, # 16 6-character base-2  strings
     unpack "b*",    # 96-character base-2  string
     "twelve bytes"; # 12-byte packed string
^Z
52|29|23|25|44|25|23|25|32|8|22|30|52|21|54|28
[download]