Append verbatim material to a file

Question

I am using the fancyvrb package. I'd like to create a verbatim-like environment that does the following two things:

1) Append the verbatim material as-is to a file that has already been opened. 2) Output the verbatim material like UseVerbatim would do.

I have tried to re-use the SaveVerbatim environment and to output the material with \immediate\write\FILE{\UseVerbatim{VERB}} but this doesn't as \UseVerbatim needs more than expansion. Adding \protect in front of \UseVerbatim didn't help either.

A non-working example follows:

\documentclass{article}
\usepackage{fancyvrb}
\newwrite\FILE
\immediate\openout\FILE=\jobname.out

\newenvironment{chunk}{%
    \VerbatimEnvironment{chunk}\begin{SaveVerbatim}[gobble=2,commentchar=\%,commandchars=\\\{\}]{VERB}%
}{%
  \end{SaveVerbatim}%
  \UseVerbatim{VERB}%
  \immediate\write\FILE{\UseVerbatim{VERB}}%
}

\begin{document}

\begin{chunk}
  First line.
  \texttt{Second} line.
\end{chunk}

\end{document}

Answer 1

Are you doing this for literate programming? If so, then maybe you want a specialized literate programming tool?

Yes, you could obviously do this by reimplementing fancyvrb.sty. Just tweak the lines containing \openout and \closeout, or even add the ability to write to an arbitrary handle as opposed to \FV@OutFile. Ain't the easiest or most robust solution though.

Instead, I've a Perl script called cat_latex_env that uses the Perl flip-flop operator .. to do exactly this :

#!/usr/bin/perl
use strict;
use warnings;

sub usage { die "Usage: cat_latex_env enviroment_name [filename]\n"; }
usage if ($#ARGV < 0);

my $env = shift;
my $begin = quotemeta "\\begin{$env}";
my $end = quotemeta "\\end{$env}";
while (<>) {
        if (/$begin/../$end/) {
                next if /$begin/ || /$end/;
                print;
        }
}

Just run cat_latex_env chunk file1.tex > file2.tex in your Makefile.