pack

pack template, list

Takes a list of values and packs it into a binary structure, returning the string containing the structure. The template is a sequence of characters that give the order and type of values, as follows:

Character	Meaning
a	An ASCII string, will be null padded
A	An ASCII string, will be space padded
b	A bit string, low-to-high order (like vec())
B	A bit string, high-to-low order
c	A signed char value
C	An unsigned char value
d	A double-precision float in the native format
f	A single-precision float in the native format
h	A hexadecimal string, low nybble first
H	A hexadecimal string, high nybble first
i	A signed integer value
I	An unsigned integer value
l	A signed long value
L	An unsigned long value
n	A short in "network" (big-endian) order
N	A long in "network" (big-endian) order
p	A pointer to a string
P	A pointer to a structure (fixed-length string)
s	A signed short value
S	An unsigned short value
v	A short in "VAX" (little-endian) order
V	A long in "VAX" (little-endian) order
u	A uuencoded string
w	A BER compressed integer
x	A null byte
X	Back up a byte
@	Null-fill to absolute position

Each character may optionally be followed by a number that gives a repeat count. Together the character and the repeat count make a field specifier. Field specifiers may be separated by whitespace, which will be ignored. With all types except a and A, the pack function will gobble up that many values from the list. Saying * for the repeat count means to use however many items are left. The a and A types gobble just one value, but pack it as a string of length count, padding with nulls or spaces as necessary. (When unpacking, A strips trailing spaces and nulls, but a does not.) Real numbers (floats and doubles) are in the native machine format only; due to the multiplicity of floating formats around, and the lack of a standard network representation, no facility for interchange has been made.

The same template may generally also be used in the unpack function. If you want to join variable length fields with a delimiter, use the join function.