conditional replace

["Thomas A. Schmitz" <thomas.schmitz@...>]

Hi all,

I'm very new to lua, so forgive me if this is trivial (or  
impossible). I want to use lua to process TeX files. Specifically, I  
want to convert some characters to Unicode, but only within a certain  
environment. I have a solution for this in perl, which is like a  
sledgehammer because extracting text from balanced delimiters is  
difficult with a regex. I was attracted to lua because its regex  
engine has the %b construct, which seems to do just what I need. What  
I want to do specifically:

Read a TeX file, convert everything inside the environment \localgreek 
{...} into Unicode, leave everything else exactly as it is and write  
the result to a new file. I think I know how to extract my passages:


for l in string.gfind(MyText,"localgreek%b{}") do
   l = string.gsub(l,'a','α')
   print(l)
end

(and so on, I want to make a table of substitutions)

But how do I write the rest of the file back? Sorry if this is a  
nobrainer, but I'm certainly not a programmer.

Thanks

Thomas