=over =item unpack TEMPLATE,EXPR C does the reverse of C: 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 C 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 %EnumberE to indicate that you want a EnumberE-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); =back