How to \immediate\write with multiple lines?

Question

Using LuaLaTeX with TeXlive 2016, although I imagine that this question applies to nearly anything:

I know how to create a file using \immediate\write on a line-by-line basis. But I would like to do it for multiple lines, where the number of lines is not known in advance (it is the result of gathering text items in a macro). Something like this:

\newwrite\file
\immediate\openout\file=pickafilename.txt
\immediate\write\file{Hello! I am a new file.}
\immediate\write\file{\MacroContainingTextMacros}
\closeout\file

The \MacroContainingTextMacros has a few small macros within it, which I wish to expand as the file is written. Each of those small macros contains a few lines of plain text. So I cannot use verbatim, or filecontents.

Any ideas?

Answer 1

You just need to write the \newlinechar which is pre-set to be ^^J in latex.

\def\MacroContainingTextMacros{
aa^^Jbb^^Jcc}
\newwrite\file
\immediate\openout\file=pickafilename.txt
\immediate\write\file{Hello!^^JI am a new file.}
\immediate\write\file{\MacroContainingTextMacros}
\closeout\file

\stop

produces

Hello!
I am a new file.
 aa
bb
cc