Is there a way to include a subset of lines from an included file using m4?

Question

Is there a way to include a subset of lines from an included file when using m4? something along the lines of include(`source.cpp', 12-15)?

I'm creating a markdown presentation using reveal.js and want to include code samples. In many cases I want to include a subset of lines from a source file. In those cases I've created a copy of the file and trimmed each copy to what should be included at each inclusion. This however leads to multiple source files which need to be updated manually if a common line changes. I want to include the same file in multiple places, specifying which lines to include at each inclusion.

I've thought of using sed but want to avoid external tools if possible. I also want to be able to specify included folders using the m4 -I option.

Suggestions on m4 macros using external tools are welcome, even if an answer using m4 only is appreciated.

Answer 1

Can-do!

define(`repeat_newline',`ifelse($1,0,,`[^
]*
repeat_newline(decr($1))')')dnl
define(`quote',``$*'')dnl
define(`include_lines',`regexp(quote(include($1)),^repeat_newline($2)`\('repeat_newline($3)`\)',`\1')')

Usage: include_lines(my_file.txt, 2, 5) reads 5 lines starting from the third line (2 is zero-indexed). It expands macros in the included file, just like include.

Answer 2

This however leads to multiple source files which need to be updated manually if a common line changes.

The main issue is how to insert the new version of a code sample (revision). That being said, you can insert fixed text calling an external command.

syscmd(`sed -n "12,15p" source.cpp')dnl

M4 rescans the inserted text after the expansion of the macro include whereas the text inserted calling sed is output literally (not parsed by M4).