example write aux.tex

\documentclass{minimal}
\usepackage{etoolbox}
\makeatletter

\newcommand{\myread}{
	\read\tempin to \myline
	\myline
	}

\newwrite\tempout
\newread\tempin



\begin{document}

\immediate\openin\tempin=mytemp.tmp
\openout\tempout=mytemp.tmp

\listadd\mylist{}
%\myread


\def\mychars{\forlistloop{, }{\mylist}}
\write\tempout{\mychars}
Scene1\\
\myread


Stuff happens
\listadd\mylist{Linda}
\listadd\mylist{Eric}


\def\mychars{\forlistloop{, }{\mylist}}
\write\tempout{\mychars}
Scene2\\
\myread

Stuff happens
\write\tempout{Mario, Caio}





\closein\tempin
\closeout\tempout
\end{document}