in reply to Re^4: dynamic extractor based off static references in file (perl)
in thread dynamic extractor based off static references in file (perl)

Argument "\0^D&" isn't numeric in sysseek

Based on those bytes/octets, to turn them a "number", it all depends on what kind ... see pack, unpack, perlpacktut

Just guessing at the right one (guessing is bad, knowing is better) 

use Data::Dump qw/ dd pp /;
dd( unpack q{c*}, "\0^D&"  );# (0, 94, 68, 38)
dd( unpack q{C*}, "\0^D&"  );# (0, 94, 68, 38)
dd( unpack q{W*}, "\0^D&"  );# (0, 94, 68, 38)
dd( unpack q{s*}, "\0^D&"  );# (24064, 9796)
dd( unpack q{S*}, "\0^D&"  );# (24064, 9796)
dd( unpack q{l*}, "\0^D&"  );# 642014720
dd( unpack q{L*}, "\0^D&"  );# 642014720
dd( unpack q{i*}, "\0^D&"  );# 642014720
dd( unpack q{I*}, "\0^D&"  );# 642014720
dd( unpack q{n*}, "\0^D&"  );# (94, 17446)
dd( unpack q{N*}, "\0^D&"  );# 6177830
dd( unpack q{v*}, "\0^D&"  );# (24064, 9796)
dd( unpack q{V*}, "\0^D&"  );# 642014720
dd( unpack q{q*}, "\0^D&"  );# ()
dd( unpack q{Q*}, "\0^D&"  );# ()

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Re^6: dynamic extractor based off static references in file (perl)
by james289o9 (Acolyte) on Dec 06, 2013 at 17:21 UTC
    Here is my code so far. 
    open(my $infile, '<', "./file") or die "Cannot open file: $!";
binmode($infile);

open(my $outfile, '>', "./reference1") or die "Cannot create file: $!"
+;
binmode($outfile);

my $buffer = '';
sysseek $infile, 0x15, 0;
sysread $infile, $buffer, 0x03;
syswrite $outfile, $buffer;
$buffer =~ s/(.)/sprintf("%x",ord($1))/eg; #this converts it into hex.
print  $buffer, "\n"; #this prints the converted $buffer (04C0)

    [download]
    Maybe I am trying to go about this the wrong way.
    $buffer = (04C0)
    It would be really nice to be able to use $buffer like this but I dont think its possible that way: 
    sysseek $infile, $buffer, 1;
sysread $infile, $new, 0x40000;
syswrite $newfile, $new;

    [download]
    Remember that $buffer contains the 04C0, which is a reference to the actual data further into the file. so I get the reference values with this: 
    my $buffer = '';
sysseek $infile, 0x15, 0;
sysread $infile, $buffer, 0x03;
syswrite $outfile, $buffer;

    [download]
    Then I try to sysseek to that position in the file like this, using the reference i obtained with the code above: 
    sysseek $infile, $buffer, 1;
sysread $infile, $new, 0x40000;
syswrite $newfile, $new;

    [download]
    Also Anonomous Monk, please let me thank you for the help so far. Im not exactly pro at programming, but I know how i want it to work, I am just having a hard time setting this up to work. I feel like i am going in circles now.
[reply]
[d/l]
[select]
      Thank you all for helping. i finally got it to work like this: 
      # this gets the reference to the actual data in the file
my $buffer = '';
sysseek $infile, 0x15, 0;
sysread $infile, $buffer, 0x03;
$buffer =~ s/(.)/sprintf("%x",ord($1))/eg;

# this will move the CUR to the actual data as specified from the refe
+rence and will extract it to file.
open(my $newfile, '>', "./file");
my $new;
sysseek $infile,hex($buffer), 0;
sysread $infile, $new, 0x40000;
syswrite $newfile, $new;

      [download]

      If you notice in the second set of sysseek, i had to hex($buffer). That solved the problem and allowed me to input "04C0" i am now extracting the data successfully.
      Thanks to everyone who took their time to help me :)
[reply]
[d/l]
        pack n An unsigned short (16-bit) in "network" (big-endian) order. 
        my $bytes = qq[\4\xC0];
my $ushortbe = unpack q[n], $bytes;
printf qq[0x%04X  0b%b  %d\n], ($ushortbe ) x 3;
__END__
0x04C0  0b10011000000  1216

        [download]

        but in all the code you've pasting you've been reading 3 bytes, a 16 bit integer takes 2 bytes ( 2x8) not 3 , so .... :)

[reply]
[d/l]
        ridiculous, but what do I care
[reply]

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