unpack - convert binary structure into normal perl variables
unpack TEMPLATE,EXPR
Unpack()
does the reverse of pack(): it takes a string representing a structure and expands it out into a list value, returning the array value. (In scalar context, it returns merely the first value produced.) The
TEMPLATE has the same format as in the
pack() function. Here's a subroutine that does substring:
sub substr { my($what,$where,$howmuch) = @_; unpack("x$where a$howmuch", $what); }
and then there's
sub ordinal { unpack("c",$_[0]); } # same as ord()
In addition, you may prefix a field with a %<number> to indicate that you want a <number>-bit checksum of the items instead of the items themselves. Default is a 16-bit checksum. For example, the following computes the same number as the System V sum program:
while (<>) { $checksum += unpack("%16C*", $_); } $checksum %= 65536;
The following efficiently counts the number of set bits in a bit vector:
$setbits = unpack("%32b*", $selectmask);
If rather than formatting bugs, you encounter substantive content errors in these documents, such as mistakes in the explanations or code, please use the perlbug utility included with the Perl distribution.