Programming Perl, 4th Edition

pack

pack TEMPLATE, LIST

This function takes a LIST of ordinary Perl values, converts them into a string of bytes according to the TEMPLATE, and returns this string. The argument list will be padded or truncated as necessary. That is, if you provide fewer arguments than the TEMPLATE requires, pack assumes additional null arguments. If you provide more arguments than the TEMPLATE requires, the extra arguments are ignored. Unrecognized format elements in TEMPLATE will raise an exception.

The template describes the structure of the string as a sequence of fields. Each field is represented by a single character that describes the type of the value and its encoding. For instance, a format character of N specifies an unsigned four-byte integer in big-endian byte order.

Fields are packed in the order given in the template. For example, to pack an unsigned one-byte integer and a single-precision floating-point value into a string, you’d say:

$string = pack("Cf", 244, 3.14);

The first byte of the returned string has the value 244. The remaining bytes are the encoding of 3.14 as a single-precision float. The particular encoding of the floating-point number depends on your computer’s hardware.

Some important things to consider when packing are:

• The type of data (such as integer or float or string)

• The range of values (such as whether your integers will fit into one, two, four, or maybe even eight bytes; or whether you’re packing 8-bit or Unicode characters)

• Whether your integers are signed or unsigned ...