Recreating a binary file from hex representation

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

I have been trying to convert a binary file to hex representation, and then taking that hex representation and recreating the binary file. I have been able to read in a binary file as hex using the following code

my $buffer;

open INFILE, "test.bin" or die "Can't open test.bin for reading: $!\n"
+;
open OUTFILE, ">test.bin" or die "Can't open test.bin for writing: $!\
+n";
select OUTFILE;

binmode INFILE;

while (read(INFILE, $buffer, 1) and printf("%X", ord($buffer))){};
print "\n";
[download]

But I am having trouble taking this hex representation and recreating the binary file with it. Here is the script I have currently that is not working

my $buffer;

open INFILE, "test.text" or die "Can't open test.txt for reading: $!\n
+";
open OUTFILE, ">test_updated.bin" or die "Can't open test_updated.bin 
+for writing: $!\n";
binmode OUTFILE;

my $line = <INFILE>;
chomp $line;
my @list = split //, $line;
my $hex_value;
my $i =1;
foreach my $character (@list)
{
  if($i%2 == 0)
  {
    $hex_value .= $character;
    syswrite OUTFILE, hex($hex_value);
  }
  elsif($i%2 == 1)
  {
    $hex_value = "0x".$character;
  }
  $i++;
}
[download]

This code just write a bunch of number to the binary file which is not what I want. Anyone have any ideas on what I am doing wrong?

Comment on Recreating a binary file from hex representation Select or Download Code

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Re: Recreating a binary file from hex representation by davido (Cardinal) on Jul 07, 2006 at 16:05 UTC
It seems like the whole thing would be easier if you used pack and unpack to convert between hex and some binary representation. perlpacktut is helpful in understanding pack and unpack. Dave	[reply]
Re: Recreating a binary file from hex representation by shmem (Chancellor) on Jul 07, 2006 at 17:42 UTC
You should use pack and unpack as was pointed out already, but the error in your script is here: `printf("%X", ord($buffer))` [download] One Byte can be 0 to FF in hex. If you have a stream of hex characters, how can you know you have 1A (26 in decimal) or two numbers, 1 and 10? say `printf("%02X", ord($buffer))` [download] to make shure each byte is represented by 2 chars (e.g. 0A for decimal 10 instead of just A). Converting back you have to read 2 Bytes each time. --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply] [d/l] [select]
Re: Recreating a binary file from hex representation by planetscape (Chancellor) on Jul 07, 2006 at 17:40 UTC
Or be lazy and use a module that does base64? ;-) HTH, planetscape	[reply]
Re: Recreating a binary file from hex representation by wazoox (Prior) on Jul 07, 2006 at 21:46 UTC
I'm working on a set of modules that read and write binary files. It's quite long, but here are the interesting parts : First, I store the data in a hash: Read more... (5 kB) Then there are a couple of subs to manage this, here is the important part for writing : sub validfields { return $_validfields } sub _packdata { #***m DataFile/_packdata # USAGE # $file->_packdata() # sérialise pour pack() tous les records # d'un fichier #* my $self = shift ; my @stringrecords ; foreach my $record_ref ( @{ $self->{records} } ) { # il faut déréférencer l'objet record avant de l'appeler my $recdata = $self->_serialize_fields( $$record_ref->getdata( +) ); push @stringrecords, $recdata if $recdata ; } @stringrecords ? return join ( '', @stringrecords ) : return } sub _serialize_fields { #*m DataFile/serialize_fields # USAGE # $file->_serialize_fields( $data_href ) # sérialise les données d'un record #*** my $self = shift ; my $data = shift ; my $output = ''; my $allfields = $self->validfields() ; # on itère sur tous les champs possibles foreach my $k ( keys %$allfields ) { # on insère la longueur en dernier next if $k eq 'LENGTH' ; my $value ; ( exists $data->{$k} ) ? ( $value = $data->{$k} ) : ( $value = + $allfields->{$k}{default} ) ; # le champ COLLATE est le seul qui soit un BYTE # les champs "noms courts" doivent contenir 0x01 # la longueur est corrigée de la longueur du format $output .= pack( $allfields->{$k}{format}. ( $allfields->{$k}{ +length} - length($allfields->{$k}{format}) + 1 ), $value ); } # on insère la longueur du champ au début my $datalength = length($output) + 5; $output = pack( "A5",$datalength ) . $output ; print $output ; return $output } [download] Hope this helps.	[reply] [d/l] [select]
Re: Recreating a binary file from hex representation by TedPride (Priest) on Jul 07, 2006 at 16:10 UTC
Or you could go the kloodge route and create a hex-to-character lookup: `@chars = (0..9, 'A'..'Z'); for (0..255) { $hex{$chars[int($_ / 16)].$chars[$_ % 16]} = chr($_); }` [download] Just feed it two hex characters and it returns the regular string character.	[reply] [d/l]


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