pack & unpack

http://blog.bigbinary.com/2011/07/20/ruby-pack-unpack.html

http://www.blackbytes.info/2017/01/read-binary-data/?tl_inbound=1&tl_target_all=1&tl_form_type=1&tl_period_type=1

unpack = String#unpack

Endian = Byte Order

MSB, LSB = bit order

1 byte = 2 nibbles = 8bits

bit

C Ascii = 67 (2^0 + 2^1 + 2^6)

'C'.unpack('b*') # LSB
# => ["11000010"]

'C'.unpack('B*') # MSB
# => ["01000011"]

String to ASCII Values

C* = 8-bit unsigned integer

"hello".unpack('C*')
=> [104, 101, 108, 108, 111]

hex

104.to_s 16 = hex value of the string.

"hello".unpack('C*').map {|e| e.to_s 16}
=> ["68", "65", "6c", "6c", "6f"]

You can also do

> "hello".unpack('H*')
=> ["68656c6c6f"]

"hello".unpack('H*') # high nibble first
=> ["68656c6c6f"]

"hello".unpack('h*')# low nibble first
=> ["8656c6c6f6"]

6 8 # high nibble first
X
8 6 # low nibble first

count

> "hello".unpack('CC')
=> [104, 101]

> "hello".unpack('CCC')
=> [104, 101, 108]

> "hello".unpack('CCCCC')
=> [104, 101, 108, 108, 111]

"aa".unpack('b8B8') # mix MSB and LSB
=> ["10000110", "01100001"]

pack = Array#pack

pack = read the stored data.

[1000001].pack('C') # binary -> 8 bit unsigned integer
=> "A"

['1000001'].pack('b*')
=> "A"

['A'].pack('H') # hex -> Ascii
=> "\xA0" # no Ascii for A0
['a'].pack('H') 
=> "\xA0" # in hex, 'A' = 'a'
['a'].pack('h')
=> "\n" # in Ascii table, '\x0A' = new line

Binary File Parsing

or parse image

binary_data     = "\x05\x00\x68\x65\x6c\x6c\x6f"
length, message = binary_data.unpack("Sa*")

# [5, "hello"]