freddo
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Mar 2, 2002, 11:53 AM
Post #1 of 9
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Needing infos on parsing...
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Hello everybody,
I'm trying to make a little (well, now it grows big) hexeditor with perl, i'd like to add a function to edit some offsets of a file and i want this to be done by parsing a text file.
This is not interactive, it parse a file, or the command line, and can do two things:
1) Output a text file from a binary file
2) From the text file, it can patch an existing binary file/create a new file.
Although it is really easy to parse one line of the definition file, i'd like to use complex structures in them. I've read Jeffrey Goff's Parse::RecDescent Tutorial and few other ressources. I was wondering if someone already used that, and if he/she can give me a (example|link|whatever_to_start_with) on how it works, it looks a little weird for me... 
Actually, a definition file for a gif may look like this:
so, the parsing is:offset packstring hash_key # a comment can be here
Quite easy to parse, a hash is populated with the values with something like:
[perl]open F, "<test.gif"; binmode F;
$_= "8 S height";
# while(<gif_file_description_here>) # {
@currentLine = split /\s+/;
### some code to remove trailling/leading spaces, comments etc etc
seek(F, $currentLine[0], 0);
$hash{$currentLine[2]} = unpack($currentLine[1], <F>);
# } # end of while
print $hash{width} ."x". $hash{height} ."\n";[/perl]
It is generaly loaded with:[perl]use frhexedit;
load($filename, \%file);[/perl]
This code is too easy, for example, gif files can hold several images and i'd like to be able to express this with rules... I dont ask for someone to do my work, i just ask for a good starting point on parsing...
Btw, i just found this nothing to do with the stuff here, but it's funny...
Thanks in advance,
Freddo
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, i cant promise i can do something on your project, but are you using parse::recdescent, or another pre-written parser, i dont feel i'm able to write a really complex parsing program in perl 
:
... perl pack is "just another way to do it" (jawtdi -- in walloon, a belgian local language, it's also a tv show). 
C-Type.txt
). 
