Modifying hex values from a script

[daviddoria]

I can use hexedit to manually edit one or two hex values in a binary file, but if I want to change many of the, this is impractical. Is there any tool that will take parameters like

someTool filename byteNumber replacementByte

?

Thanks,

David

[ni_boy]

You could try awk, it's bloody powerful, but I've never actually cracked it in any real sense..... Personally I would write a quick perl script.
for a quick & dirty, have it move the file to .bak (or whatever), open the file, read binary char by char, output to the original filename & replace the char you want when it gets to it.
This code has basics you need to proccess the files & deal with the hex chars. You can fill it out for full function:

open INFILE, "$infile";
binmode (INFILE);
open OUTFILE,">$outfile";
 binmode (OUTFILE);
$replace=pack("H2",$hextext);
while (read(INFILE, $buffer, 1)){
  $data = sprintf("%02X",ord($buffer));
  $charcount++;
  if ($charcount == $location){
     print OUTFILE $replace;
  }else{
     print OUTFILE pack("H2",$data);
  }
}
close INFILE;
close OUTFILE;

cheers

[VirtualLinuxUser]

Ni_boy, is the script you've given in bash, PERL or AWK?

[ni_boy]

perl.
obviously you'll need to do you own variable assignment, etc.
Also, that's basically pulled from something I wrote where I was scanning files. If you wanted to replace a single byte in a specific loc there's probably a function for it in perl when writing binary mode, so the script could be a lot simpler.
cheers