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+# Packed \Data
+
+## Quick Reference
+
+These tables summarize the directives for packing and unpacking.
+
+### For Integers
+
+| Directive | Meaning |
+|-----------------------|-----------------------------------------------------------------------------------------------------|
+| `C` | 8-bit unsigned (`unsigned char`) |
+| `S` | 16-bit unsigned, native endian (`uint16_t`) |
+| `L` | 32-bit unsigned, native endian (`uint32_t`) |
+| `Q` | 64-bit unsigned, native endian (`uint64_t`) |
+| `J` | pointer width unsigned, native endian (`uintptr_t`) |
+| | |
+| `c` | 8-bit signed (`signed char`) |
+| `s` | 16-bit signed, native endian (`int16_t`) |
+| `l` | 32-bit signed, native endian (`int32_t`) |
+| `q` | 64-bit signed, native endian (`int64_t`) |
+| `j` | pointer width signed, native endian (`intptr_t`) |
+| | |
+| `S_` `S!` | `unsigned short`, native endian |
+| `I` `I_` `I!` | `unsigned int`, native endian |
+| `L_` `L!` | `unsigned long`, native endian |
+| `Q_` `Q!` | `unsigned long long`, native endian; (raises ArgumentError if the platform has no `long long` type) |
+| `J!` | `uintptr_t`, native endian (same with `J`) |
+| | |
+| `s_` `s!` | `signed short`, native endian |
+| `i` `i_` `i!` | `signed int`, native endian |
+| `l_` `l!` | `signed long`, native endian |
+| `q_` `q!` | `signed long long`, native endian; (raises ArgumentError if the platform has no `long long` type) |
+| `j!` | `intptr_t`, native endian (same with `j`) |
+| | |
+| `S>` `s>` `S!>` `s!>` | each the same as the directive without `>`, but big endian; `S>` is the same as `n` |
+| `L>` `l>` `L!>` `l!>` | `L>` is the same as `N` |
+| `I!>` `i!>` | |
+| `Q>` `q>` `Q!>` `q!>` | |
+| `J>` `j>` `J!>` `j!>` | |
+| | |
+| `S<` `s<` `S!<` `s!<` | each the same as the directive without `<`, but little endian; `S<` is the same as `v` |
+| `L<` `l<` `L!<` `l!<` | `L<` is the same as `V` |
+| `I!<` `i!<` | |
+| `Q<` `q<` `Q!<` `q!<` | |
+| `J<` `j<` `J!<` `j!<` | |
+| | |
+| `n` | 16-bit unsigned, network (big-endian) byte order |
+| `N` | 32-bit unsigned, network (big-endian) byte order |
+| `v` | 16-bit unsigned, VAX (little-endian) byte order |
+| `V` | 32-bit unsigned, VAX (little-endian) byte order |
+| | |
+| `U` | UTF-8 character |
+| `w` | BER-compressed integer |
+| `R` | LEB128 encoded unsigned integer |
+| `r` | LEB128 encoded signed integer |
+
+### For Floats
+
+| Directive | Meaning |
+|-----------|---------------------------------------------------|
+| `D` `d` | double-precision, native format |
+| `F` `f` | single-precision, native format |
+| `E` | double-precision, little-endian byte order |
+| `e` | single-precision, little-endian byte order |
+| `G` | double-precision, network (big-endian) byte order |
+| `g` | single-precision, network (big-endian) byte order |
+
+### For Strings
+
+| Directive | Meaning |
+|-----------|------------------------------------------------------------------------------------------------|
+| `A` | arbitrary binary string (remove trailing nulls and ASCII spaces) |
+| `a` | arbitrary binary string |
+| `Z` | null-terminated string |
+| `B` | bit string (MSB first) |
+| `b` | bit string (LSB first) |
+| `H` | hex string (high nibble first) |
+| `h` | hex string (low nibble first) |
+| `u` | UU-encoded string |
+| `M` | quoted-printable, MIME encoding (see RFC2045) |
+| `m` | base64 encoded string (RFC 2045) (default) (base64 encoded string (RFC 4648) if followed by 0) |
+| `P` | pointer to a structure (fixed-length string) |
+| `p` | pointer to a null-terminated string |
+
+### Additional Directives for Packing
+
+| Directive | Meaning |
+|-----------|----------------------------|
+| `@` | moves to absolute position |
+| `X` | back up a byte |
+| `x` | null byte |
+
+### Additional Directives for Unpacking
+
+| Directive | Meaning |
+|-----------|-------------------------------------------------|
+| `@` | skip to the offset given by the length argument |
+| `X` | skip backward one byte |
+| `x` | skip forward one byte |
+| `^` | return the current offset |
+
+## Packing and Unpacking
+
+Certain Ruby core methods deal with packing and unpacking data:
+
+- Method Array#pack:
+ Formats each element in array `self` into a binary string;
+ returns that string.
+- Method String#unpack:
+ Extracts data from string `self`,
+ forming objects that become the elements of a new array;
+ returns that array.
+- Method String#unpack1:
+ Does the same, but unpacks and returns only the first extracted object.
+
+Each of these methods accepts a string `template`,
+consisting of zero or more _directive_ characters,
+each followed by zero or more _modifier_ characters.
+
+Examples (directive `'C'` specifies '`unsigned character`'):
+
+```ruby
+[65].pack('C') # => "A" # One element, one directive.
+[65, 66].pack('CC') # => "AB" # Two elements, two directives.
+[65, 66].pack('C') # => "A" # Extra element is ignored.
+[65].pack('') # => "" # No directives.
+[65].pack('CC') # Extra directive raises ArgumentError.
+```
+
+```ruby
+'A'.unpack('C') # => [65] # One character, one directive.
+'AB'.unpack('CC') # => [65, 66] # Two characters, two directives.
+'AB'.unpack('C') # => [65] # Extra character is ignored.
+'A'.unpack('CC') # => [65, nil] # Extra directive generates nil.
+'AB'.unpack('') # => [] # No directives.
+```
+
+The string `template` may contain any mixture of valid directives
+(directive `'c'` specifies 'signed character'):
+
+```ruby
+[65, -1].pack('cC') # => "A\xFF"
+"A\xFF".unpack('cC') # => [65, 255]
+```
+
+The string `template` may contain whitespace (which is ignored)
+and comments, each of which begins with character `'#'`
+and continues up to and including the next following newline:
+
+```ruby
+[0,1].pack(" C #foo \n C ") # => "\x00\x01"
+"\0\1".unpack(" C #foo \n C ") # => [0, 1]
+```
+
+Any directive may be followed by either of these modifiers:
+
+- `'*'` - The directive is to be applied as many times as needed:
+
+ ```ruby
+ [65, 66].pack('C*') # => "AB"
+ 'AB'.unpack('C*') # => [65, 66]
+ ```
+
+- \Integer `count` - The directive is to be applied `count` times:
+
+ ```ruby
+ [65, 66].pack('C2') # => "AB"
+ [65, 66].pack('C3') # Raises ArgumentError.
+ 'AB'.unpack('C2') # => [65, 66]
+ 'AB'.unpack('C3') # => [65, 66, nil]
+ ```
+
+ Note: Directives in `%w[A a Z m]` use `count` differently;
+ see [\String Directives][rdoc-ref:@String+Directives].
+
+If elements don't fit the provided directive, only least significant bits are encoded:
+
+```ruby
+[257].pack("C").unpack("C") # => [1]
+```
+
+## Packing Method
+
+Method Array#pack accepts optional keyword argument
+`buffer` that specifies the target string (instead of a new string):
+
+```ruby
+[65, 66].pack('C*', buffer: 'foo') # => "fooAB"
+```
+
+The method can accept a block:
+
+```ruby
+# Packed string is passed to the block.
+[65, 66].pack('C*') {|s| p s } # => "AB"
+```
+
+## Unpacking Methods
+
+Methods String#unpack and String#unpack1 each accept
+an optional keyword argument `offset` that specifies an offset
+into the string:
+
+```ruby
+'ABC'.unpack('C*', offset: 1) # => [66, 67]
+'ABC'.unpack1('C*', offset: 1) # => 66
+```
+
+Both methods can accept a block:
+
+```ruby
+# Each unpacked object is passed to the block.
+ret = []
+"ABCD".unpack("C*") {|c| ret << c }
+ret # => [65, 66, 67, 68]
+```
+
+```ruby
+# The single unpacked object is passed to the block.
+'AB'.unpack1('C*') {|ele| p ele } # => 65
+```
+
+## \Integer Directives
+
+Each integer directive specifies the packing or unpacking
+for one element in the input or output array.
+
+### 8-Bit \Integer Directives
+
+- `'c'` - 8-bit signed integer
+ (like C `signed char`):
+
+ ```ruby
+ [0, 1, 255].pack('c*') # => "\x00\x01\xFF"
+ s = [0, 1, -1].pack('c*') # => "\x00\x01\xFF"
+ s.unpack('c*') # => [0, 1, -1]
+ ```
+
+- `'C'` - 8-bit unsigned integer
+ (like C `unsigned char`):
+
+ ```ruby
+ [0, 1, 255].pack('C*') # => "\x00\x01\xFF"
+ s = [0, 1, -1].pack('C*') # => "\x00\x01\xFF"
+ s.unpack('C*') # => [0, 1, 255]
+ ```
+
+### 16-Bit \Integer Directives
+
+- `'s'` - 16-bit signed integer, native-endian
+ (like C `int16_t`):
+
+ ```ruby
+ [513, -514].pack('s*') # => "\x01\x02\xFE\xFD"
+ s = [513, 65022].pack('s*') # => "\x01\x02\xFE\xFD"
+ s.unpack('s*') # => [513, -514]
+ ```
+
+- `'S'` - 16-bit unsigned integer, native-endian
+ (like C `uint16_t`):
+
+ ```ruby
+ [513, -514].pack('S*') # => "\x01\x02\xFE\xFD"
+ s = [513, 65022].pack('S*') # => "\x01\x02\xFE\xFD"
+ s.unpack('S*') # => [513, 65022]
+ ```
+
+- `'n'` - 16-bit network integer, big-endian:
+
+ ```ruby
+ s = [0, 1, -1, 32767, -32768, 65535].pack('n*')
+ # => "\x00\x00\x00\x01\xFF\xFF\x7F\xFF\x80\x00\xFF\xFF"
+ s.unpack('n*')
+ # => [0, 1, 65535, 32767, 32768, 65535]
+ ```
+
+- `'v'` - 16-bit VAX integer, little-endian:
+
+ ```ruby
+ s = [0, 1, -1, 32767, -32768, 65535].pack('v*')
+ # => "\x00\x00\x01\x00\xFF\xFF\xFF\x7F\x00\x80\xFF\xFF"
+ s.unpack('v*')
+ # => [0, 1, 65535, 32767, 32768, 65535]
+ ```
+
+### 32-Bit \Integer Directives
+
+- `'l'` - 32-bit signed integer, native-endian
+ (like C `int32_t`):
+
+ ```ruby
+ s = [67305985, -50462977].pack('l*')
+ # => "\x01\x02\x03\x04\xFF\xFE\xFD\xFC"
+ s.unpack('l*')
+ # => [67305985, -50462977]
+ ```
+
+- `'L'` - 32-bit unsigned integer, native-endian
+ (like C `uint32_t`):
+
+ ```ruby
+ s = [67305985, 4244504319].pack('L*')
+ # => "\x01\x02\x03\x04\xFF\xFE\xFD\xFC"
+ s.unpack('L*')
+ # => [67305985, 4244504319]
+ ```
+
+- `'N'` - 32-bit network integer, big-endian:
+
+ ```ruby
+ s = [0,1,-1].pack('N*')
+ # => "\x00\x00\x00\x00\x00\x00\x00\x01\xFF\xFF\xFF\xFF"
+ s.unpack('N*')
+ # => [0, 1, 4294967295]
+ ```
+
+- `'V'` - 32-bit VAX integer, little-endian:
+
+ ```ruby
+ s = [0,1,-1].pack('V*')
+ # => "\x00\x00\x00\x00\x01\x00\x00\x00\xFF\xFF\xFF\xFF"
+ s.unpack('v*')
+ # => [0, 0, 1, 0, 65535, 65535]
+ ```
+
+### 64-Bit \Integer Directives
+
+- `'q'` - 64-bit signed integer, native-endian
+ (like C `int64_t`):
+
+ ```ruby
+ s = [578437695752307201, -506097522914230529].pack('q*')
+ # => "\x01\x02\x03\x04\x05\x06\a\b\xFF\xFE\xFD\xFC\xFB\xFA\xF9\xF8"
+ s.unpack('q*')
+ # => [578437695752307201, -506097522914230529]
+ ```
+
+- `'Q'` - 64-bit unsigned integer, native-endian
+ (like C `uint64_t`):
+
+ ```ruby
+ s = [578437695752307201, 17940646550795321087].pack('Q*')
+ # => "\x01\x02\x03\x04\x05\x06\a\b\xFF\xFE\xFD\xFC\xFB\xFA\xF9\xF8"
+ s.unpack('Q*')
+ # => [578437695752307201, 17940646550795321087]
+ ```
+
+### Platform-Dependent \Integer Directives
+
+- `'i'` - Platform-dependent width signed integer,
+ native-endian (like C `int`):
+
+ ```ruby
+ s = [67305985, -50462977].pack('i*')
+ # => "\x01\x02\x03\x04\xFF\xFE\xFD\xFC"
+ s.unpack('i*')
+ # => [67305985, -50462977]
+ ```
+
+- `'I'` - Platform-dependent width unsigned integer,
+ native-endian (like C `unsigned int`):
+
+ ```ruby
+ s = [67305985, -50462977].pack('I*')
+ # => "\x01\x02\x03\x04\xFF\xFE\xFD\xFC"
+ s.unpack('I*')
+ # => [67305985, 4244504319]
+ ```
+
+- `'j'` - Pointer-width signed integer, native-endian
+ (like C `intptr_t`):
+
+ ```ruby
+ s = [67305985, -50462977].pack('j*')
+ # => "\x01\x02\x03\x04\x00\x00\x00\x00\xFF\xFE\xFD\xFC\xFF\xFF\xFF\xFF"
+ s.unpack('j*')
+ # => [67305985, -50462977]
+ ```
+
+- `'J'` - Pointer-width unsigned integer, native-endian
+ (like C `uintptr_t`):
+
+ ```ruby
+ s = [67305985, 4244504319].pack('J*')
+ # => "\x01\x02\x03\x04\x00\x00\x00\x00\xFF\xFE\xFD\xFC\x00\x00\x00\x00"
+ s.unpack('J*')
+ # => [67305985, 4244504319]
+ ```
+
+### Other \Integer Directives
+
+- `'U'` - UTF-8 character:
+
+ ```ruby
+ s = [4194304].pack('U*')
+ # => "\xF8\x90\x80\x80\x80"
+ s.unpack('U*')
+ # => [4194304]
+ ```
+
+- `'r'` - Signed LEB128-encoded integer
+ (see [Signed LEB128](https://en.wikipedia.org/wiki/LEB128#Signed_LEB128))
+
+ ```ruby
+ s = [1, 127, -128, 16383, -16384].pack("r*")
+ # => "\x01\xFF\x00\x80\x7F\xFF\xFF\x00\x80\x80\x7F"
+ s.unpack('r*')
+ # => [1, 127, -128, 16383, -16384]
+ ```
+
+- `'R'` - Unsigned LEB128-encoded integer
+ (see [Unsigned LEB128](https://en.wikipedia.org/wiki/LEB128#Unsigned_LEB128))
+
+ ```ruby
+ s = [1, 127, 128, 16383, 16384].pack("R*")
+ # => "\x01\x7F\x80\x01\xFF\x7F\x80\x80\x01"
+ s.unpack('R*')
+ # => [1, 127, 128, 16383, 16384]
+ ```
+
+- `'w'` - BER-encoded integer
+ (see [BER encoding](https://en.wikipedia.org/wiki/X.690#BER_encoding)):
+
+ ```ruby
+ s = [1073741823].pack('w*')
+ # => "\x83\xFF\xFF\xFF\x7F"
+ s.unpack('w*')
+ # => [1073741823]
+ ```
+
+### Modifiers for \Integer Directives
+
+For the following directives, `'!'` or `'_'` modifiers may be
+suffixed as underlying platform’s native size.
+
+- `'i'`, `'I'` - C `int`, always native size.
+- `'s'`, `'S'` - C `short`.
+- `'l'`, `'L'` - C `long`.
+- `'q'`, `'Q'` - C `long long`, if available.
+- `'j'`, `'J'` - C `intptr_t`, always native size.
+
+Native size modifiers are silently ignored for always native size directives.
+
+The endian modifiers also may be suffixed in the directives above:
+
+- `'>'` - Big-endian.
+- `'<'` - Little-endian.
+
+## \Float Directives
+
+Each float directive specifies the packing or unpacking
+for one element in the input or output array.
+
+### Single-Precision \Float Directives
+
+- `'F'` or `'f'` - Native format:
+
+ ```ruby
+ s = [3.0].pack('F') # => "\x00\x00@@"
+ s.unpack('F') # => [3.0]
+ ```
+
+- `'e'` - Little-endian:
+
+ ```ruby
+ s = [3.0].pack('e') # => "\x00\x00@@"
+ s.unpack('e') # => [3.0]
+ ```
+
+- `'g'` - Big-endian:
+
+ ```ruby
+ s = [3.0].pack('g') # => "@@\x00\x00"
+ s.unpack('g') # => [3.0]
+ ```
+
+### Double-Precision \Float Directives
+
+- `'D'` or `'d'` - Native format:
+
+ ```ruby
+ s = [3.0].pack('D') # => "\x00\x00\x00\x00\x00\x00\b@"
+ s.unpack('D') # => [3.0]
+ ```
+
+- `'E'` - Little-endian:
+
+ ```ruby
+ s = [3.0].pack('E') # => "\x00\x00\x00\x00\x00\x00\b@"
+ s.unpack('E') # => [3.0]
+ ```
+
+- `'G'` - Big-endian:
+
+ ```ruby
+ s = [3.0].pack('G') # => "@\b\x00\x00\x00\x00\x00\x00"
+ s.unpack('G') # => [3.0]
+ ```
+
+A float directive may be infinity or not-a-number:
+
+```ruby
+inf = 1.0/0.0 # => Infinity
+[inf].pack('f') # => "\x00\x00\x80\x7F"
+"\x00\x00\x80\x7F".unpack('f') # => [Infinity]
+
+nan = inf/inf # => NaN
+[nan].pack('f') # => "\x00\x00\xC0\x7F"
+"\x00\x00\xC0\x7F".unpack('f') # => [NaN]
+```
+
+## \String Directives
+
+Each string directive specifies the packing or unpacking
+for one byte in the input or output string.
+
+### Binary \String Directives
+
+- `'A'` - Arbitrary binary string (space padded; count is width);
+ `nil` is treated as the empty string:
+
+ ```ruby
+ ['foo'].pack('A') # => "f"
+ ['foo'].pack('A*') # => "foo"
+ ['foo'].pack('A2') # => "fo"
+ ['foo'].pack('A4') # => "foo "
+ [nil].pack('A') # => " "
+ [nil].pack('A*') # => ""
+ [nil].pack('A2') # => " "
+ [nil].pack('A4') # => " "
+ ```
+
+ ```ruby
+ "foo\0".unpack('A') # => ["f"]
+ "foo\0".unpack('A4') # => ["foo"]
+ "foo\0bar".unpack('A10') # => ["foo\x00bar"] # Reads past "\0".
+ "foo ".unpack('A') # => ["f"]
+ "foo ".unpack('A4') # => ["foo"]
+ "foo".unpack('A4') # => ["foo"]
+ ```
+
+ ```ruby
+ japanese = 'こんにちは'
+ japanese.size # => 5
+ japanese.bytesize # => 15
+ [japanese].pack('A') # => "\xE3"
+ [japanese].pack('A*') # => "\xE3\x81\x93\xE3\x82\x93\xE3\x81\xAB\xE3\x81\xA1\xE3\x81\xAF"
+ japanese.unpack('A') # => ["\xE3"]
+ japanese.unpack('A2') # => ["\xE3\x81"]
+ japanese.unpack('A4') # => ["\xE3\x81\x93\xE3"]
+ japanese.unpack('A*') # => ["\xE3\x81\x93\xE3\x82\x93\xE3\x81\xAB\xE3\x81\xA1\xE3\x81\xAF"]
+ ```
+
+- `'a'` - Arbitrary binary string (null padded; count is width):
+
+ ```ruby
+ ["foo"].pack('a') # => "f"
+ ["foo"].pack('a*') # => "foo"
+ ["foo"].pack('a2') # => "fo"
+ ["foo\0"].pack('a4') # => "foo\x00"
+ [nil].pack('a') # => "\x00"
+ [nil].pack('a*') # => ""
+ [nil].pack('a2') # => "\x00\x00"
+ [nil].pack('a4') # => "\x00\x00\x00\x00"
+ ```
+
+ ```ruby
+ "foo\0".unpack('a') # => ["f"]
+ "foo\0".unpack('a4') # => ["foo\x00"]
+ "foo ".unpack('a4') # => ["foo "]
+ "foo".unpack('a4') # => ["foo"]
+ "foo\0bar".unpack('a4') # => ["foo\x00"] # Reads past "\0".
+ ```
+
+- `'Z'` - Same as `'a'`,
+ except that null is added or ignored with `'*'`:
+
+ ```ruby
+ ["foo"].pack('Z*') # => "foo\x00"
+ [nil].pack('Z*') # => "\x00"
+ ```
+
+ ```ruby
+ "foo\0".unpack('Z*') # => ["foo"]
+ "foo".unpack('Z*') # => ["foo"]
+ "foo\0bar".unpack('Z*') # => ["foo"] # Does not read past "\0".
+ ```
+
+### Bit \String Directives
+
+- `'B'` - Bit string (high byte first):
+
+ ```ruby
+ ['11111111' + '00000000'].pack('B*') # => "\xFF\x00"
+ ['10000000' + '01000000'].pack('B*') # => "\x80@"
+ ```
+
+ ```ruby
+ ['1'].pack('B0') # => ""
+ ['1'].pack('B1') # => "\x80"
+ ['1'].pack('B2') # => "\x80\x00"
+ ['1'].pack('B3') # => "\x80\x00"
+ ['1'].pack('B4') # => "\x80\x00\x00"
+ ['1'].pack('B5') # => "\x80\x00\x00"
+ ['1'].pack('B6') # => "\x80\x00\x00\x00"
+ ```
+
+ ```ruby
+ "\xff\x00".unpack("B*") # => ["1111111100000000"]
+ "\x01\x02".unpack("B*") # => ["0000000100000010"]
+ ```
+
+ ```ruby
+ "".unpack("B0") # => [""]
+ "\x80".unpack("B1") # => ["1"]
+ "\x80".unpack("B2") # => ["10"]
+ "\x80".unpack("B3") # => ["100"]
+ ```
+
+- `'b'` - Bit string (low byte first):
+
+ ```ruby
+ ['11111111' + '00000000'].pack('b*') # => "\xFF\x00"
+ ['10000000' + '01000000'].pack('b*') # => "\x01\x02"
+ ```
+
+ ```ruby
+ ['1'].pack('b0') # => ""
+ ['1'].pack('b1') # => "\x01"
+ ['1'].pack('b2') # => "\x01\x00"
+ ['1'].pack('b3') # => "\x01\x00"
+ ['1'].pack('b4') # => "\x01\x00\x00"
+ ['1'].pack('b5') # => "\x01\x00\x00"
+ ['1'].pack('b6') # => "\x01\x00\x00\x00"
+ ```
+
+ ```ruby
+ "\xff\x00".unpack("b*") # => ["1111111100000000"]
+ "\x01\x02".unpack("b*") # => ["1000000001000000"]
+ ```
+
+ ```ruby
+ "".unpack("b0") # => [""]
+ "\x01".unpack("b1") # => ["1"]
+ "\x01".unpack("b2") # => ["10"]
+ "\x01".unpack("b3") # => ["100"]
+ ```
+
+### Hex \String Directives
+
+- `'H'` - Hex string (high nibble first):
+
+ ```ruby
+ ['10ef'].pack('H*') # => "\x10\xEF"
+ ['10ef'].pack('H0') # => ""
+ ['10ef'].pack('H3') # => "\x10\xE0"
+ ['10ef'].pack('H5') # => "\x10\xEF\x00"
+ ```
+
+ ```ruby
+ ['fff'].pack('H3') # => "\xFF\xF0"
+ ['fff'].pack('H4') # => "\xFF\xF0"
+ ['fff'].pack('H5') # => "\xFF\xF0\x00"
+ ['fff'].pack('H6') # => "\xFF\xF0\x00"
+ ['fff'].pack('H7') # => "\xFF\xF0\x00\x00"
+ ['fff'].pack('H8') # => "\xFF\xF0\x00\x00"
+ ```
+
+ ```ruby
+ "\x10\xef".unpack('H*') # => ["10ef"]
+ "\x10\xef".unpack('H0') # => [""]
+ "\x10\xef".unpack('H1') # => ["1"]
+ "\x10\xef".unpack('H2') # => ["10"]
+ "\x10\xef".unpack('H3') # => ["10e"]
+ "\x10\xef".unpack('H4') # => ["10ef"]
+ "\x10\xef".unpack('H5') # => ["10ef"]
+ ```
+
+- `'h'` - Hex string (low nibble first):
+
+ ```ruby
+ ['10ef'].pack('h*') # => "\x01\xFE"
+ ['10ef'].pack('h0') # => ""
+ ['10ef'].pack('h3') # => "\x01\x0E"
+ ['10ef'].pack('h5') # => "\x01\xFE\x00"
+ ```
+
+ ```ruby
+ ['fff'].pack('h3') # => "\xFF\x0F"
+ ['fff'].pack('h4') # => "\xFF\x0F"
+ ['fff'].pack('h5') # => "\xFF\x0F\x00"
+ ['fff'].pack('h6') # => "\xFF\x0F\x00"
+ ['fff'].pack('h7') # => "\xFF\x0F\x00\x00"
+ ['fff'].pack('h8') # => "\xFF\x0F\x00\x00"
+ ```
+
+ ```ruby
+ "\x01\xfe".unpack('h*') # => ["10ef"]
+ "\x01\xfe".unpack('h0') # => [""]
+ "\x01\xfe".unpack('h1') # => ["1"]
+ "\x01\xfe".unpack('h2') # => ["10"]
+ "\x01\xfe".unpack('h3') # => ["10e"]
+ "\x01\xfe".unpack('h4') # => ["10ef"]
+ "\x01\xfe".unpack('h5') # => ["10ef"]
+ ```
+
+### Pointer \String Directives
+
+- `'P'` - Pointer to a structure (fixed-length string):
+
+ ```ruby
+ s = ['abc'].pack('P') # => "\xE0O\x7F\xE5\xA1\x01\x00\x00"
+ s.unpack('P*') # => ["abc"]
+ ".".unpack("P") # => []
+ ("\0" * 8).unpack("P") # => [nil]
+ [nil].pack("P") # => "\x00\x00\x00\x00\x00\x00\x00\x00"
+ ```
+
+- `'p'` - Pointer to a null-terminated string:
+
+ ```ruby
+ s = ['abc'].pack('p') # => "(\xE4u\xE5\xA1\x01\x00\x00"
+ s.unpack('p*') # => ["abc"]
+ ".".unpack("p") # => []
+ ("\0" * 8).unpack("p") # => [nil]
+ [nil].pack("p") # => "\x00\x00\x00\x00\x00\x00\x00\x00"
+ ```
+
+### Other \String Directives
+
+- `'M'` - Quoted printable, MIME encoding;
+ text mode, but input must use LF and output LF;
+ (see [RFC 2045](https://www.ietf.org/rfc/rfc2045.txt)):
+
+ ```ruby
+ ["a b c\td \ne"].pack('M') # => "a b c\td =\n\ne=\n"
+ ["\0"].pack('M') # => "=00=\n"
+ ```
+
+ ```ruby
+ ["a"*1023].pack('M') == ("a"*73+"=\n")*14+"a=\n" # => true
+ ("a"*73+"=\na=\n").unpack('M') == ["a"*74] # => true
+ (("a"*73+"=\n")*14+"a=\n").unpack('M') == ["a"*1023] # => true
+ ```
+
+ ```ruby
+ "a b c\td =\n\ne=\n".unpack('M') # => ["a b c\td \ne"]
+ "=00=\n".unpack('M') # => ["\x00"]
+ ```
+
+ ```ruby
+ "pre=31=32=33after".unpack('M') # => ["pre123after"]
+ "pre=\nafter".unpack('M') # => ["preafter"]
+ "pre=\r\nafter".unpack('M') # => ["preafter"]
+ "pre=".unpack('M') # => ["pre="]
+ "pre=\r".unpack('M') # => ["pre=\r"]
+ "pre=hoge".unpack('M') # => ["pre=hoge"]
+ "pre==31after".unpack('M') # => ["pre==31after"]
+ "pre===31after".unpack('M') # => ["pre===31after"]
+ ```
+
+- `'m'` - Base64 encoded string;
+ count specifies input bytes between each newline,
+ rounded down to nearest multiple of 3;
+ if count is zero, no newlines are added;
+ (see [RFC 4648](https://www.ietf.org/rfc/rfc4648.txt)):
+
+ ```ruby
+ [""].pack('m') # => ""
+ ["\0"].pack('m') # => "AA==\n"
+ ["\0\0"].pack('m') # => "AAA=\n"
+ ["\0\0\0"].pack('m') # => "AAAA\n"
+ ["\377"].pack('m') # => "/w==\n"
+ ["\377\377"].pack('m') # => "//8=\n"
+ ["\377\377\377"].pack('m') # => "////\n"
+ ```
+
+ ```ruby
+ "".unpack('m') # => [""]
+ "AA==\n".unpack('m') # => ["\x00"]
+ "AAA=\n".unpack('m') # => ["\x00\x00"]
+ "AAAA\n".unpack('m') # => ["\x00\x00\x00"]
+ "/w==\n".unpack('m') # => ["\xFF"]
+ "//8=\n".unpack('m') # => ["\xFF\xFF"]
+ "////\n".unpack('m') # => ["\xFF\xFF\xFF"]
+ "A\n".unpack('m') # => [""]
+ "AA\n".unpack('m') # => ["\x00"]
+ "AA=\n".unpack('m') # => ["\x00"]
+ "AAA\n".unpack('m') # => ["\x00\x00"]
+ ```
+
+ ```ruby
+ [""].pack('m0') # => ""
+ ["\0"].pack('m0') # => "AA=="
+ ["\0\0"].pack('m0') # => "AAA="
+ ["\0\0\0"].pack('m0') # => "AAAA"
+ ["\377"].pack('m0') # => "/w=="
+ ["\377\377"].pack('m0') # => "//8="
+ ["\377\377\377"].pack('m0') # => "////"
+ ```
+
+ ```ruby
+ "".unpack('m0') # => [""]
+ "AA==".unpack('m0') # => ["\x00"]
+ "AAA=".unpack('m0') # => ["\x00\x00"]
+ "AAAA".unpack('m0') # => ["\x00\x00\x00"]
+ "/w==".unpack('m0') # => ["\xFF"]
+ "//8=".unpack('m0') # => ["\xFF\xFF"]
+ "////".unpack('m0') # => ["\xFF\xFF\xFF"]
+ ```
+
+- `'u'` - UU-encoded string:
+
+ ```ruby
+ [""].pack("u") # => ""
+ ["a"].pack("u") # => "!80``\n"
+ ["aaa"].pack("u") # => "#86%A\n"
+ ```
+
+ ```ruby
+ "".unpack("u") # => [""]
+ "#86)C\n".unpack("u") # => ["abc"]
+ ```
+
+## Offset Directives
+
+- `'@'` - Begin packing at the given byte offset;
+ for packing, null fill or shrink if necessary:
+
+ ```ruby
+ [1, 2].pack("C@0C") # => "\x02"
+ [1, 2].pack("C@1C") # => "\x01\x02"
+ [1, 2].pack("C@5C") # => "\x01\x00\x00\x00\x00\x02"
+ [*1..5].pack("CCCC@2C") # => "\x01\x02\x05"
+ ```
+
+ For unpacking, cannot to move to outside the string:
+
+ ```ruby
+ "\x01\x00\x00\x02".unpack("C@3C") # => [1, 2]
+ "\x00".unpack("@1C") # => [nil]
+ "\x00".unpack("@2C") # Raises ArgumentError.
+ ```
+
+- `'X'` - For packing, shrink for the given byte offset:
+
+ ```ruby
+ [0, 1, 2].pack("CCXC") # => "\x00\x02"
+ [0, 1, 2].pack("CCX2C") # => "\x02"
+ ```
+
+ For unpacking; rewind unpacking position for the given byte offset:
+
+ ```ruby
+ "\x00\x02".unpack("CCXC") # => [0, 2, 2]
+ ```
+
+ Cannot to move to outside the string:
+
+ ```ruby
+ [0, 1, 2].pack("CCX3C") # Raises ArgumentError.
+ "\x00\x02".unpack("CX3C") # Raises ArgumentError.
+ ```
+
+- `'x'` - Begin packing at after the given byte offset;
+ for packing, null fill if necessary:
+
+ ```ruby
+ [].pack("x0") # => ""
+ [].pack("x") # => "\x00"
+ [].pack("x8") # => "\x00\x00\x00\x00\x00\x00\x00\x00"
+ ```
+
+ For unpacking, cannot to move to outside the string:
+
+ ```ruby
+ "\x00\x00\x02".unpack("CxC") # => [0, 2]
+ "\x00\x00\x02".unpack("x3C") # => [nil]
+ "\x00\x00\x02".unpack("x4C") # Raises ArgumentError
+ ```
+
+- `'^'` - Only for unpacking; the current position:
+
+ ```ruby
+ "foo\0\0\0".unpack("Z*^") # => ["foo", 4]
+ ```
generated by cgit v1.2.3 (git 2.25.1) at 2026-06-03 12:57:17 +0000