/ Ruby
/
method

unpack

v1_9_3_125 - Show latest stable - Class: String
unpack(p1)
public

Decodes str (which may contain binary data) according to the format string, returning an array of each value extracted. The format string consists of a sequence of single-character directives, summarized in the table at the end of this entry. Each directive may be followed by a number, indicating the number of times to repeat with this directive. An asterisk (“*”) will use up all remaining elements. The directives sSiIlL may each be followed by an underscore (“_”) or exclamation mark (“!”) to use the underlying platform’s native size for the specified type; otherwise, it uses a platform-independent consistent size. Spaces are ignored in the format string. See also Array#pack.

"abc \0\0abc \0\0".unpack('A6Z6')   #=> ["abc", "abc "]
"abc \0\0".unpack('a3a3')           #=> ["abc", " \000\000"]
"abc \0abc \0".unpack('Z*Z*')       #=> ["abc ", "abc "]
"aa".unpack('b8B8')                 #=> ["10000110", "01100001"]
"aaa".unpack('h2H2c')               #=> ["16", "61", 97]
"\xfe\xff\xfe\xff".unpack('sS')     #=> [-2, 65534]
"now=20is".unpack('M*')             #=> ["now is"]
"whole".unpack('xax2aX2aX1aX2a')    #=> ["h", "e", "l", "l", "o"]

This table summarizes the various formats and the Ruby classes returned by each.

Integer | | Directive | Returns | Meaning

C         | Integer | 8-bit unsigned (unsigned char)
S         | Integer | 16-bit unsigned, native endian (uint16_t)
L         | Integer | 32-bit unsigned, native endian (uint32_t)
Q         | Integer | 64-bit unsigned, native endian (uint64_t)
          |         |
c         | Integer | 8-bit signed (signed char)
s         | Integer | 16-bit signed, native endian (int16_t)
l         | Integer | 32-bit signed, native endian (int32_t)
q         | Integer | 64-bit signed, native endian (int64_t)
          |         |
S_, S!    | Integer | unsigned short, native endian
I, I_, I! | Integer | unsigned int, native endian
L_, L!    | Integer | unsigned long, native endian
          |         |
s_, s!    | Integer | signed short, native endian
i, i_, i! | Integer | signed int, native endian
l_, l!    | Integer | signed long, native endian
          |         |
S> L> Q>  | Integer | same as the directives without ">" except
s> l> q>  |         | big endian
S!> I!>   |         | (available since Ruby 1.9.3)
L!> Q!>   |         | "S>" is same as "n"
s!> i!>   |         | "L>" is same as "N"
l!> q!>   |         |
          |         |
S< L< Q<  | Integer | same as the directives without "<" except
s< l< q<  |         | little endian
S!< I!<   |         | (available since Ruby 1.9.3)
L!< Q!<   |         | "S<" is same as "v"
s!< i!<   |         | "L<" is same as "V"
l!< q!<   |         |
          |         |
n         | Integer | 16-bit unsigned, network (big-endian) byte order
N         | Integer | 32-bit unsigned, network (big-endian) byte order
v         | Integer | 16-bit unsigned, VAX (little-endian) byte order
V         | Integer | 32-bit unsigned, VAX (little-endian) byte order
          |         |
U         | Integer | UTF-8 character
w         | Integer | BER-compressed integer (see Array.pack)

Float | | Directive | Returns | Meaning

D, d      | Float   | double-precision, native format
F, f      | Float   | single-precision, native format
E         | Float   | double-precision, little-endian byte order
e         | Float   | single-precision, little-endian byte order
G         | Float   | double-precision, network (big-endian) byte order
g         | Float   | single-precision, network (big-endian) byte order

String | | Directive | Returns | Meaning

A         | String  | arbitrary binary string (remove trailing nulls and ASCII spaces)
a         | String  | arbitrary binary string
Z         | String  | null-terminated string
B         | String  | bit string (MSB first)
b         | String  | bit string (LSB first)
H         | String  | hex string (high nibble first)
h         | String  | hex string (low nibble first)
u         | String  | UU-encoded string
M         | String  | quoted-printable, MIME encoding (see RFC2045)
m         | String  | base64 encoded string (RFC 2045) (default)
          |         | base64 encoded string (RFC 4648) if followed by 0
P         | String  | pointer to a structure (fixed-length string)
p         | String  | pointer to a null-terminated string

Misc. | | Directive | Returns | Meaning

@         | ---     | skip to the offset given by the length argument
X         | ---     | skip backward one byte
x         | ---     | skip forward one byte