pack  ('a8',"hello")       produce "hello\0\0\0"
    pack  ('Z8',"hello")       produce "hello\0\0\0"
    pack  ('A8',"hello")       produce "hello   "   
    unpack('a8',"hello\0\0\0") produce "hello\0\0\0"
    unpack('Z8',"hello\0\0\0") produce "hello"
    unpack('A8',"hello   ")    produce "hello"
    unpack('A8',"hello\0\0\0") produce "hello"