Quines

Everybody loves a good quine. The most obvious, and most cheating way to write a “quine” In LaTeX is to use the listings package.

\documentclass{article}
\usepackage{listings}
\lstset{language=[LaTeX]TeX}
\begin{document}
\lstinputlisting{\jobname}
\end{document}

This is not very exciting and it's cheating on two levels. One, a quine is not supposed to read its source code. So just as

#!/bin/sh
cat "$0"

is not a quine, using the listings package is not a quine. Secondly, a quine should produce code that can be compiled directly. As it stands, I know of no TeX implementation that will read the code from a typeset pdf.

This is the shortest quine (give or take the characters used to construct the output file name) that I could construct.

\toks0{\immediate\openout2\jobname.copy.tex\def\t{\immediate\write2{\string
\toks0{\the\toks0}\string\the\string\toks0\end}}\t}\the\toks0\end

One thing to note is that due to the way TeX parses and displays tokens, this is not technically a quine. As with most quines on the Internet, this is a quine generator. Run it once to produce a quine:

$ tex quine
This is TeX, Version 3.1415926 (TeX Live 2010)
(./quine.tex )
No pages of output.
Transcript written on quine.log.
$ tex quine.copy
This is TeX, Version 3.1415926 (TeX Live 2010)
(./quine.copy.tex )
No pages of output.
Transcript written on quine.copy.log.
$ diff -s quine.copy.tex quine.copy.copy.tex
Files quine.copy.tex and quine.copy.copy.tex are identical