Write to file: using a macro as the filename

Question

I'm setting a complex user manual, made of several independant documents. For the overall TOC, I want each document to write some data into a file which is then parsed by the TOC file later.

Here's the point: I want to use a string in a macro as the filename, but it doesn't work. It must have something to do with correct expansion, but I can't find the error...

\documentclass[10pt]{article}

 \newcommand{\docnr}{foo bar}

 \usepackage{stringstrings}
 \newcommand{\tocfile}{../toc/\noblanks{\docnr}.tex}

 \newcommand{\SToc}{
   \newwrite\tempfile
   \immediate\openout\tempfile=\tocfile

   %other stuff
   \immediate\write\tempfile{\docnr}
   %other stuff

   \immediate\closeout\tempfile
}

\begin{document}
   \SToc
   Hello World.
\end{document}

EDIT: A completely different approach that would work for me would be the following: I'm looking for an environment that's full content is expanded as much as possible and then written to the file. By this, I could simply \input it in the TOC later. Something like

\newcommand{\docnr}{foo bar}
\begin{writetofile}[../toc/\noblanks{\docnr}.tex]
   \textbf{\docnr}
\end{writetofile}

And the file foobar.tex would contain

\textbf{foo bar}

There are many environments to write commands verbatim (without expansion) to a file - I've now searched for the exact opposite, but couldn't find anything. Grmpf!

Answer 1

The LaTeX kernel has a command \zap@space, which is expandable and can be used in file names, e.g.:

\newcommand*{\docnr}{foo bar}

\makeatletter
\edef\docnr@wosp{\docnr\space}
\newcommand{\tocfile}{}
\edef\tocfile{../toc/\expandafter\zap@space\docnr@wosp\@empty.tex}
\makeatother

\typeout{[tocfile=\tocfile]}

Result:

[tocfile=../toc/foobar.tex]

Writing without page numbers

When page numbers are not needed, then deferred writing is not needed and we can use \immediate\write. LaTeX's protection mechanism is supported by

\let\protect\noexpand

while writing the entry. Then \textbf{\docnr} becomes \textbf {foo bar}. TeX adds a space after command names and the other space comes from LaTeX's protected commands, which expand to a macro with the same name except that a trailing space was added to the macro name.

Fragile macros can be protected by prefixing it with \protect as usual. \string can also be used, it avoids the space after the command name.

\documentclass{article}

\newcommand*{\docnr}{foo bar}

\makeatletter
\edef\docnr@wosp{\docnr\space}
\newcommand{\tocfile}{}
\edef\tocfile{\expandafter\zap@space\docnr@wosp\@empty.tex}
\makeatother

% toc file management
\makeatletter
\if@filesw
  \let\toc@handle\relax
  \DeclareRobustCommand{\addtotoc}[1]{%
    \ifx\toc@handle\relax
      \newwrite\toc@handle
      \immediate\openout\toc@handle=\tocfile\relax
    \fi
    \begingroup
      \let\protect\noexpand
      \immediate\write\toc@handle{#1}%
    \endgroup
  }%
  \newcommand*{\closetoc}{%
    \immediate\closeout\toc@handle
  }%
\else
  \newcommand{\addtotoc}[1]{}%
  \newcommand*{\closetoc}{}%
\fi
\makeatother

\begin{document}
  \addtotoc{\textbf{\docnr}, %
    written via macro \string\verb|\string\addtotoc|.}
  \closetoc
  \input{\tocfile}
\end{document}

File foobar.tex:

\textbf  {foo bar}, written via macro \verb|\addtotoc|.

The file can be read before the first \addtotoc and after \closetoc.

Deferred writing with page numbers

\documentclass{article}

\newcommand*{\docnr}{foo bar}

\makeatletter
\edef\docnr@wosp{\docnr\space}
\newcommand{\tocfile}{}
\edef\tocfile{\expandafter\zap@space\docnr@wosp\@empty.tex}
\makeatother

% toc file management
\makeatletter
\if@filesw
  \let\toc@handle\relax
  \DeclareRobustCommand*{\addtotoc}{%
    \ifx\toc@handle\relax
      \newwrite\toc@handle
      \immediate\openout\toc@handle=\tocfile\relax
    \fi
    \protected@write\toc@handle{}% + argument of \addtotoc
  }%
  \newcommand*{\closetoc}{%
    \closeout\toc@handle
  }%
\else
  \newcommand{\addtotoc}[1]{}%
  \newcommand*{\closetoc}{}%
\fi
\makeatother

\begin{document}
  Hello World!

  \addtotoc{\textbf{\docnr} on page \thepage,
    written via macro \string\verb|\string\addtotoc|.}
  \closetoc
  \newpage
  \input{\tocfile}
\end{document}

File foobar.tex:

\textbf  {foo bar} on page 1, written via macro \verb|\addtotoc|.

The file can be read before the first \addtotoc and after the page, where the deferred \closeout is called.

Answer 2

You could try this with xstring and \StrDel, preprocessing the filename first and storing it to \tocfile macro.

The macro \noblanks from stringstrings isn't expandable, unfortunately. (Have a look into stringstrings package or use texdef to see this)

Some other note: It might occur that pdflatex will refuse to write on pathnames starting with a ..

Try to locate texmf.cnf and add this line at the end:

openout_any = a

However, this might be a security breach.

\documentclass[10pt]{article}


\newwrite\tempfile

\newcommand{\docnr}{foo bar}

%\usepackage{stringstrings}
\usepackage{xstring}
\gdef\tocfile{}
\StrDel[0]{../toc/\docnr.tex}{ }[\tocfile]


\newcommand{\SToc}{%
  \immediate\openout\tempfile=\tocfile
  % other stuff
  \immediate\write\tempfile{\docnr}
  % other stuff
  \immediate\closeout\tempfile
}

\begin{document}
\SToc
Hello World.
\end{document}

Answer 3

See Can filecontents write an external file in a parent directory? for the problem of writing files in directories above the current one or given an explicit path.

This said, we can solve your problem with an easy set of macros in expl3:

\documentclass{article}

\usepackage{xparse}

\ExplSyntaxOn

\iow_new:N \g_victor_output_stream

\tl_new:N \l_victor_filename_tl

%\tl_const:Nn \c_victor_prefix_tl { ../toc/ } % use this one
\tl_const:Nn \c_victor_prefix_tl { ./ } % for the test

\cs_generate_variant:Nn \iow_open:Nn { NV }

\NewDocumentCommand{\SToc}{ O{\docnr} }
 {
  \tl_set:Nx \l_victor_filename_tl { \c_victor_prefix_tl #1 }
  \tl_replace_all:Nnn \l_victor_filename_tl { ~ } { }
  \iow_open:NV \g_victor_output_stream \l_victor_filename_tl
  \STocStuffA
  \iow_now:Nx \g_victor_output_stream { #1 }
  \STocStuffB
  \iow_close:N \g_victor_output_stream
 }
\ExplSyntaxOff

\newcommand{\docnr}{foo bar}

\newcommand{\STocStuffA}{} % for the test
\newcommand{\STocStuffB}{} % for the test

\begin{document}

\SToc

Hello World.

\end{document}

The macros \STocStuffA and \STocStuffB will contain what you need to be done before and after the write operation as hinted in your code.

Just change the prefix to get a location different from the current working directory (the one where the main TeX file belongs).

You can call \SToc with no optional argument or with one, that will be used instead of the default \docnr. Possibly you don't need this feature, but it's so easy to add it that I didn't want to lose this opportunity for adding flexibility to your macros.

We prepare the string to be passed to \openout (in expl3 it becomes \iow_open:Nn, which we use a variant of) by removing all spaces. In the write operation, we can directly use the argument (\docnr by default).

---

Note about your code: don't put the \newwrite declaration in the macro \SToc, because you'd waste an output stream at each call. So \newwrite\tempfile must go outside the definition of \SToc (and a more specific name than \tempfile should be used).