Compile two versions of a document from the same latex source - latex

Question

How to automatically compile two versions of the same document, for example version without answers for the students and another version with answers for myself?

Answer 1

I have a small bash script to do a dual format.
function latex-ans () {
n=$(basename $1 .tex) # strip .tex in filename foo.tex -> foo
ln -s $n.tex $n-ans.tex # create a soft link (for instance foo-ans.tex -> foo.tex)
pdflatex '\def\withanswer{1} \input{'$n-ans'}' && pdflatex $n
% first format the version with answers and then the normal version
rm $n-ans.tex $n-ans.log
% remove useless files
}
If I have a file foo.tex, this commands formats both versions of the file and generates two pdf: foo.pdf and foo-ans.pdf. Thanks to the renaming of foo.tex through the ln -s, it also keeps separate foo.aux and foo-ans.aux to preserve useful information on both versions.
At the latex level, I basically do the same and use the macro \withanswers to configure my packages.

Answer 2

There are several packages that allow to conditionally exclude certain parts of the document, for example the exercise package.
With TeXstudio, the following magic comment can be used to automatically compile both versions at once (including repeated compilation for cross-references, bibliographies, indices etc.):
% !TeX program = latexmk -pdf -pdflatex="pdflatex -synctex=1 -interaction=nonstopmode -shell-escape" -jobname=% -pretex="\newcommand{\version}{noanswer}" -usepretex % | latexmk -pdf -pdflatex="pdflatex -synctex=1 -interaction=nonstopmode -shell-escape" -jobname=%_solution -pretex="\newcommand{\version}{}" -usepretex % | txs:///view-pdf "?am)_solution.pdf"
\documentclass{article}
% setting a default value in case it is compiled without the magic comment
\ifdefined\version
\else
\def\version{noanswer}
\fi
\usepackage[\version]{exercise}
\begin{document}
\begin{Exercise}[title={Title},label=ex1]
question text
\end{Exercise}
\begin{Answer}[ref={ex1}]
solution
\end{Answer}
\end{document}