Commandline for pdflatex:
pdflatex main.tex "\def\anonymous{}\include{main}"
main.tex:
\documentclass[a4paper]{article}
\begin{document}
\ifx\anonymous\undefined
Lorem ipsum dolor sit amet
\else
Nam eu velit eget neque mollis imperdiet
\fi
\end{document}
The above command line will make PDF file which holds "Lorem ipsum dolor sit amet".
How can I make the output to hold "Nam eu velit eget neque mollis imperdiet"?