examples of pack function in Perl Monday, January 17, 2011

$foo = pack("WWWW",65,66,67,68);
# foo eq "ABCD"
$foo = pack("W4",65,66,67,68);
# same thing
$foo = pack("W4",0x24b6,0x24b7,0x24b8,0x24b9);
# same thing with Unicode circled letters.
$foo = pack("U4",0x24b6,0x24b7,0x24b8,0x24b9);
# same thing with Unicode circled letters. You don't get the UTF-8
# bytes because the U at the start of the format caused a switch to
# U0-mode, so the UTF-8 bytes get joined into characters
$foo = pack("C0U4",0x24b6,0x24b7,0x24b8,0x24b9);
# foo eq "\xe2\x92\xb6\xe2\x92\xb7\xe2\x92\xb8\xe2\x92\xb9"
# This is the UTF-8 encoding of the string in the previous example

$foo = pack("ccxxcc",65,66,67,68);
# foo eq "AB\0\0CD"

# NOTE: The examples above featuring "W" and "c" are true
# only on ASCII and ASCII-derived systems such as ISO Latin 1
# and UTF-8. On EBCDIC systems, the first example would be
# $foo = pack("WWWW",193,194,195,196);

$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)

$utmp_template = "Z8 Z8 Z16 L";
$utmp = pack($utmp_template, @utmp1);
# a struct utmp (BSDish)

@utmp2 = unpack($utmp_template, $utmp);
# "@utmp1" eq "@utmp2"

sub bintodec {
unpack("N", pack("B32", substr("0" x 32 . shift, -32)));
}

$foo = pack('sx2l', 12, 34);
# short 12, two zero bytes padding, long 34
$bar = pack('s@4l', 12, 34);
# short 12, zero fill to position 4, long 34
# $foo eq $bar
$baz = pack('s.l', 12, 4, 34);
# short 12, zero fill to position 4, long 34

$foo = pack('nN', 42, 4711);
# pack big-endian 16- and 32-bit unsigned integers
$foo = pack('S>L>', 42, 4711);
# exactly the same
$foo = pack('s<', -42, 4711);
# pack little-endian 16- and 32-bit signed integers
$foo = pack('(sl)<', -42, 4711);
# exactly the same


ref to http://perldoc.perl.org/functions/pack.html