3.2.182 unpack

unpack 

TEMPLATE

, 

EXPR

This function does the reverse of pack : it takes a string ( EXPR ) representing a data structure and expands it out into a list value, returning the list value. (In a scalar context, it can be used to unpack a single value.) The TEMPLATE has much the same format as in the pack function - it specifies the order and type of the values to be unpacked. (See pack for a more detailed description of TEMPLATE .)

Here's a subroutine that does (some of) substr , only slower:

sub substr {     my($what, $where, $howmuch) = @_;     if ($where < 0) {         $where = -$where;         return unpack "\@* X$where a$howmuch", $what;     }     else {         return unpack "x$where a$howmuch", $what;     } }

and then there's:

sub signed_ord { unpack "c", shift }

Here's a complete uudecode program:

#!/usr/bin/perl $_ = <> until ($mode,$file) = /^begin\s*(\d*)\s*(\S*)/; open(OUT,"> $file") if $file ne ""; while (<>) {     last if /^end/;     next if /[a-z]/;     next unless int((((ord() - 32) & 077) + 2) / 3) ==                 int(length() / 4);     print OUT unpack "u", $_; } chmod oct $mode, $file;

In addition, you may prefix a field with % number to indicate that you want it to return 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:

undef $/; $checksum = unpack ("%32C*", <>) % 32767;

The following efficiently counts the number of set bits in a bit vector:

$setbits = unpack "%32b*", $selectmask;

Here's a simple MIME decoder:

while (<>) {   tr#A-Za-z0-9+/##cd;                   # remove non-base64 chars   tr#A-Za-z0-9+/# -_#;                  # convert to uuencoded format   $len = pack("c", 32 + 0.75*length);   # compute length byte   print unpack("u", $len . $_);         # uudecode and print }