How to use luatex callbacks to generate a verbatim copy of the input file

Question

I'm trying to devise a LuaTeX solution for the question Extracting the contents of text in a specified environment into a new file, but it is turning more difficult than expected.

To begin, I need to solve a problem which seemed simple enough, but I'm unable to solve properly. I want to use some of the LuaTeX callbacks or hooks to dump into a file a copy of each line of the main document file.

My first approach was to hook into process_input_buffer, with this code:

-- luafuncions.lua
f = io.open(tex.jobname .. "-copy.tex", "w")

letpass = function(line)
    f:write(line.."\n")
  return nil
end
callback.register("process_input_buffer",letpass)

When I use the following tex document:

\directlua{dofile("luafunctions.lua")}
% Example.tex
\documentclass{article}
\usepackage{fontspec}
\usepackage{lipsum}

\begin{document}
1. \lipsum[1]
2. \lipsum[2]
3. \lipsum[3]
\end{document}

And compile it through lualatex, I get:

1. The expected Example.pdf file in which all looks correct
2. The file Example-copy.tex which I expected to contain a copy of Example.tex (except perhaps for the first line)

However, I get a 1.4Mb file (gasp!) which starts and ends with:

% Example.tex
\documentclass{article}
\usepackage{fontspec}
%%
%% This is file `article.cls',
%% generated with the docstrip utility.

%... 33750 lines omitted

\begin{document}

%... 4874 lines omitted

1. \lipsum[1]
2. \lipsum[2]
3. \lipsum[3]
\end{document}
\relax

So, sort of worked :-) But I guess that what is happening is that all the lines read from .cls, .sty, .def, .aux etc... are being processed by the calback too, and thus they are being dumped.

I want to avoid that. So I hoped that I could hook some other callback to the event of an external file being open (and closed), and set a boolean to let my function know that it should not write those parts.

However I cannot figure which callback can be useful to do this. Callbacks open_read_file and close look promising, but apparently I have to provide a reader if I use those callbacks. I would hoped that if my hooks returned nil, the default readers will be used, but it is not that way.

Is there a simple solution for this problem?

Answer 1

You can do this without a callback but maybe you need one for some reason. If not, then the following works (as far as I can tell):

--luafunctions.lua

myout = io.open(tex.jobname.."-copy.tex", "w")
myin = io.open(tex.jobname..".tex", "r")
for line in myin:lines() do 
    myout:write(line.."\n")
end
myout:close()
myin:close()

With your main .tex being.

\directlua{dofile("luafunctions.lua")}
\documentclass{article}
\usepackage{fontspec}
\usepackage{lipsum}

% Example.tex
\begin{document}
1. \lipsum[1]
2. \lipsum[2]
3. \lipsum[3]
\end{document}

Also, there is some code here that might help with your original goal.