Question

this might be quite a newbie question, but i need to process a certain text file and dump its content into a binary file and i do not know how – i decided to use perl, but my perl skills are quite low. I probably should have written this in C++, but this seem like a nice and easy task for perl, so why not learn something new? 😉 The text file has thousands of lines in this format:

2A02FC42 4

You can look at it as a hexadecimal number (the length is ALWAYS 8) and a regular number. Now i need to dump all the lines into a binary file in this format (it should look like this when viewed with a hex editor):

42FC022A00000004

More examples so it is clear:

70726F67 36 -> 676F727000000024
6A656374 471 -> 7463656A000001D7

The part of parsing the input file is easy, but i’m stuck on the second part, where i should write this into a binary file. I have no idea how to format the data in this way or even how to output things in binary mode. Can someone help me out here?

Thanks.

EDIT: updated the examples, forgot about endiannes – im on a LE system.

Answer 1

Use pack:

#! /usr/bin/perl

use warnings;
use strict;

# demo only    
*ARGV = *DATA;

while (<>) {
  my($a,$b) = split;
  $a = join "", reverse $a =~ /(..)/g;
  $b = sprintf "%08x", $b;

  print pack "H*" => $a . $b;
}

__DATA__
2A02FC42 4
70726F67 36
6A656374 471

Sample run:

$ ./prog.pl | od -t x1
0000000 42 fc 02 2a 00 00 00 04 67 6f 72 70 00 00 00 24
0000020 74 63 65 6a 00 00 01 d7
0000030