Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I've never been too good with pack/unpack myself and every time I find the need to use them, I spend hours trudging through docs figuring it out. I accept this as being one of my own personal roadblocks, but I will soon find myself working with people who have no experience with them, and little experience with perl.

I'd rather it not be a blind-leading-the-blind sort of thing, and have been searching for a tutorial that covers (or links to coverage of) everything a junior programmer from A higher-level language wouldn't be familiar with, such as hex nybbles, big and little endians, bitwise operations, and so on.

Does anyone know of such an in-depth guide?

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Re: Definitive guide to pack/unpack?
by chargrill (Parson) on Apr 10, 2007 at 14:13 UTC
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Re: Definitive guide to pack/unpack?
by polettix (Vicar) on Apr 10, 2007 at 14:52 UTC
    As already said in the article already pointed by chargrill, the official documentation has a tutorial of its own: perlpacktut. It's quite comprehensive and easy to read - and to forget :)

    <blatant_promotion>Just in case... there is also an Italian translation.</blatant_promotion>

    Flavio
    perl -ple'$_=reverse' <<<ti.xittelop@oivalf

    Don't fool yourself.
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[select]
Re: Definitive guide to pack/unpack?
by Anonymous Monk on Apr 10, 2007 at 20:04 UTC
    i'm trying to use unpack to read what is essentially a memory dump of several c variables, and i think perhaps i've overestimated the power of unpack...how far off am I? 
    # should unpack to:
#   an int32 (4 byte) value of -1
#   a char (1 byte) value of 'A'
#   a null-terminated string value of "ANOTHER"
#   a null-terminated string value of "CSTRING"
$packed_string = "\xFF\xFF\xFF\xFF"
               . "\x41"
               . "\x41\x4e\x4f\x54\x48\x45\x52\x00"
               . "\x43\x53\x54\x52\x49\x4e\x47\x00";

# should just be able to plug in some kind of
# format for unpack, right?
($int,$char,$another,$cstring)
  = unpack('',$packed_string );

    [download]
    would i instead have to put together subs like get_int(), get_char(), and get_cstring(), calling each of them in the order needed? if so, could I still use pack to make life easier?
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[d/l]

      What problem are you encountering? 

      #! perl -slw
use strict;
# should unpack to:
#   an int32 (4 byte) value of -1
#   a char (1 byte) value of 'A'
#   a null-terminated string value of "ANOTHER"
#   a null-terminated string value of "CSTRING"
my $packed_string = "\xFF\xFF\xFF\xFF"
               . "\x41"
               . "\x41\x4e\x4f\x54\x48\x45\x52\x00"
               . "\x43\x53\x54\x52\x49\x4e\x47\x00";

# should just be able to plug in some kind of
# format for unpack, right?
my ($int,$char,$another,$cstring)  = unpack('l A1 Z* Z*',$packed_strin
+g );

print "int: $int Char:$char String:$another String:$cstring";

__END__
c:\test>junk7
int: -1 Char:A String:ANOTHER String:CSTRING

      [download]
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
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