($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = gmtime(time);All array elements are numeric, and come straight out of a struct tm. In particular this means that $mon has the range 0..11 and $wday has the range 0..6. If EXPR is omitted, does gmtime(time).
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime(time);All array elements are numeric, and come straight out of a struct tm. In particular this means that $mon has the range 0..11 and $wday has the range 0..6. If EXPR is omitted, does localtime(time).
$val = oct($val) if $val =~ /^0/;If EXPR is omitted, uses $_.
A An ascii string, will be space padded. a An ascii string, will be null padded. c A signed char value. C An unsigned char value. s A signed short value. S An unsigned short value. 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" order. N A long in "network" order. f A single-precision float in the native format. d A double-precision float in the native format. p A pointer to a string. v A short in "VAX" (little-endian) order. V A long in "VAX" (little-endian) order. x A null byte. X Back up a byte. @ Null fill to absolute position. u A uuencoded string. b A bit string (ascending bit order, like vec()). B A bit string (descending bit order). h A hex string (low nybble first). H A hex string (high nybble first).Each letter may optionally be followed by a number which gives a repeat count. With all types except "a", "A", "b", "B", "h" and "H", the pack function will gobble up that many values from the LIST. A * 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.) Likewise, the "b" and "B" fields pack a string that many bits long. The "h" and "H" fields pack a string that many nybbles long. 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. This means that packed floating point data written on one machine may not be readable on another - even if both use IEEE floating point arithmetic (as the endian-ness of the memory representation is not part of the IEEE spec). Note that perl uses doubles internally for all numeric calculation, and converting from double -> float -> double will lose precision (i.e. unpack("f", pack("f", $foo)) will not in general equal $foo).
Examples:
$foo = pack("cccc",65,66,67,68); # foo eq "ABCD" $foo = pack("c4",65,66,67,68); # same thing $foo = pack("ccxxcc",65,66,67,68); # foo eq "AB\0\0CD" $foo = pack("s2",1,2); # "\1\0\2\0" on little-endian # "\0\1\0\2" on big-endian $foo = pack("a4","abcd","x","y","z"); # "abcd" $foo = pack("aaaa","abcd","x","y","z"); # "axyz" $foo = pack("a14","abcdefg"); # "abcdefg\0\0\0\0\0\0\0" $foo = pack("i9pl", gmtime); # a real struct tm (on my system anyway) sub bintodec { unpack("N", pack("B32", substr("0" x 32 . shift, -32))); }The same template may generally also be used in the unpack function.
sub substr { local($what,$where,$howmuch) = @_; unpack("x$where a$howmuch", $what); } and then there's sub ord { unpack("c",$_[0]); }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;
Vectors created with vec() can also be manipulated with the logical operators |, & and ^, which will assume a bit vector operation is desired when both operands are strings. This interpretation is not enabled unless there is at least one vec() in your program, to protect older programs.
To transform a bit vector into a string or array of 0's and 1's, use these:
$bits = unpack("b*", $vector); @bits = split(//, unpack("b*", $vector));If you know the exact length in bits, it can be used in place of the *.