How can I automatically add document sectioning information to the log file?

Question

Is it possible to add data into the .log file?

For example, I create a LaTeX file and at some point, i want to put a command that will add data into the .log file.

I don't want something hardcoded into the LaTeX file. I want to add a message like, "You are now parsing section 1". Then somewhere else in the document, I want to add "You are now parsing section 2".

Is it possible, if yes, how can I achieve this?

Answer 1

Like I suggested in my answer to your other question, you can hook into the \section macro. The issue is that \section is not a simple macro. Its expansion involves an auxiliary macro \@startsection, which in turn expands \@sect with eight arguments. You can read Section 61.2 of source2e for the gory details, but the first argument is the "level" of section (section, subsection, etc.), and the eighth is the name of the section.

You need a TeX executable with the e-TeX primitives to use the etoolbox package. But you probably do without knowing it. The code below adds to the \@sect command the logging directive. It essentially does what David and Werner suggested in their comments, but automatically after each sectioning command.

\documentclass{article}
\usepackage{lipsum}
\usepackage{etoolbox}

\makeatletter
\apptocmd{\@sect}{
   \typeout{You are now parsing #1 \expandafter\csname the#1\endcsname, ``#8''}
}
{%
   \typeout{Patch of \string\@sect\space succeeded}
}
{%
   \typeout{Patch of \string\@sect\space failed}
}
\makeatother

\begin{document}

\section{First}
\lipsum[1-2]

\subsection{A subsection}
\lipsum[3-7]

\section{Second}
\lipsum

\section{Third}
\lipsum

\end{document}

Here is a snippet from the console output:

(/usr/local/texlive/2012/texmf-dist/tex/latex/base/article.cls
Document Class: article 2007/10/19 v1.4h Standard LaTeX document class
(/usr/local/texlive/2012/texmf-dist/tex/latex/base/size10.clo))
(/usr/local/texlive/2012/texmf-dist/tex/latex/lipsum/lipsum.sty)
(/usr/local/texlive/2012/texmf-dist/tex/latex/etoolbox/etoolbox.sty
(/usr/local/texlive/2012/texmf-dist/tex/latex/etex-pkg/etex.sty))
Patch of \@sect succeeded
(./Pete.aux)
You are now parsing section 1, ``First''
You are now parsing subsection 1.1, ``A subsection''
[1{/usr/local/texlive/2012/texmf-var/fonts/map/pdftex/updmap/pdftex.map}]
You are now parsing section 2, ``Second''
[2]
You are now parsing section 3, ``Third''
[3] [4] [5] (./Pete.aux) )</usr/local/texlive/2012/texmf-dist/fonts/type1/publi
c/amsfonts/cm/cmbx12.pfb></usr/local/texlive/2012/texmf-dist/fonts/type1/public
/amsfonts/cm/cmr10.pfb>
Output written on Pete.pdf (5 pages, 41359 bytes).
Transcript written on Pete.log.