This question is purely academic. TeXing a file containing
\valign{\halign#\cr!
causes an ! Emergency stop. error. Is that the shortest code which produces a fatal error in TeX?
asked Oct 14, 2011 at 0:50
5 Answers
\def\a{a\a}\a
EDIT: Shorter version, as suggested by Bruno:
\def~{~~}~
This gives I can't go on meeting you like this:
\halign{#&&#\cr\multispan{300}}
And this gives This can't happen:
\halign{#&&#\cr\multispan{300}\cr}
answered Oct 14, 2011 at 1:32
-
1Good idea. That doesn't cause
Emergency stop., butTeX capacity exceeded, sorry [main memory size=...].And you can shorten that by 3 characters using the fact that~is active by default in TeX. I suspect thatThis can't happen.is harder to achieve :). Oct 14, 2011 at 22:27 -
I was not very clear in my question, so it was a little bit tricky to decide which answer to accept. I am choosing this answer, because it is the only one that genuinely crashes TeX when run in
errorstopmode. Other solutions go tobatchmode(ornonstopmode) and can thus crash TeX much more easily (e.g., with an empty file). Oct 19, 2011 at 21:08 -
2@LevBishop -- congratulations! this is the first "simple" code i've ever seen that reliably produces
This can't happen.unfortunately, it depends on extensions added by e-tex. i'm still looking for an example that will reliably produceThis can't happen.with knuth's unextended engine. although such an example will probably not result in changes to the tex engine, it would definitely result in wider recognition and "glory" of a sort. Jun 15, 2012 at 13:24 -
@LevBishop -- the code with
\a, on an unextended tex, results inTeX capacity exceeded, sorry [main memory size=327145], and the code with the tildes results inTeX capacity exceeded, sorry [input stack size=200]. (this has already been pointed out by Bruno Le Floch.) both tested onVersion 3.14159 [PD VMS 3.6]. nice try, but i claim this isn't a valid winner. Jun 15, 2012 at 13:54 -
@barbarabeeton are you sure that my
This can't happenexample requires e-tex? I see that the same code path is present in my "Computers & Typesetting/B: TeX:The Program" book (which describes version 3.14159), in section 798 (with the comment{this can happen, but won't}). I don't haveVersion 3.14159 [PD VMS 3.6]but withVersion 3.1415926 (MiKTeX 2.9 64-bit)which doesn't seem to understand e-tex primitives such as\eTeXversionit still givesThis can't happen. I do agree that no changes to the TeX engine are required here, though :) Jun 15, 2012 at 15:33
A file just consisting of ^H (IIRC the only character with catcode invalid by default in LaTeX) will do it:
[1 1016] ~/temp % echo -e '\b' | latex
This is pdfTeX, Version 3.1415926-2.3-1.40.12 (TeX Live 2011)
**entering extended mode
! Text line contains an invalid character.
<*> ^^H
?
! Emergency stop.
<*> ^^H
No pages of output.
Transcript written on texput.log.
[1 1017] ~/temp %
answered Oct 14, 2011 at 6:23
-
7
-
-
2@You: I'm not actually sure it is; but
^His the backspace character and if you find explicit backspace characters in your text file, something's wrong with your terminal and/od editor :) Oct 14, 2011 at 9:02 -
6Many characters are invalid in LaTeX (try
\newcount\foo\loop\message{\the\catcode\foo}\advance\foo1\iftrue\repeat). I think the key reason why this crashes TeX is that somehow it is called in batch mode (e.g., putting an invalid character in a file and running TeX on it will simply prompt you for more material). Thus,echo "" | latexalso crashes, with a different error message. Oct 14, 2011 at 22:25 -
4but this requires a response to the
?prompt. the original challenge was to create a tex file that stops all by itself, no intervention. Jun 15, 2012 at 14:08
{
Here's the log:
This is TeX, Version 3.1415926 (TeX Live 2011) (format=tex 2011.8.28) 14 OCT 2011 11:17
**short
(./short.tex)
! Emergency stop.
<*> short
*** (job aborted, no legal \end found)
No pages of output.
If running with -interaction=batchmode is allowed then I win: just try
touch inexistent.tex
tex -interaction=batchmode inexistent
and you'll get
This is TeX, Version 3.1415926 (TeX Live 2011) (format=tex 2011.8.28) 14 OCT 2011 11:25
**inexistent.tex
(./inexistent.tex)
! Emergency stop.
<*> inexistent.tex
*** (job aborted, no legal \end found)
No pages of output.
The output of the shell to check:
> ls -l inexistent.tex
-rw-r--r-- 1 enricomb staff 0 Oct 14 11:25 inexistent.tex
-
2I think your first example is also run in
batchmode, because simply doingtex short.texleaves me with TeX prompting me for more data. I think that-interaction=batchmodeshould be counted towards the number of characters :). Oct 14, 2011 at 22:19 -
2@BrunoLeFloch The
{example works also innonstopmode. But you're right: skimming through "TeX, the program" tells that the only fatal errors inerrorstopmodeare of the "interwoven alignment" kind.– egregOct 14, 2011 at 22:35 -
@egreg -- run with unextended tex, this hangs with a
*prompt waiting for a response. i'm not sure how to specify\nonstopmodeon a vms installation except by putting the command in the tex file, but when that's done, it does result inemergency stop.Jun 15, 2012 at 14:05 -
@barbarabeeton Do you still use a TeX on a VMS system? Sorry, but I can't test it, as my last experience on VMS was in 1993. :) Maybe
TEX /Nor something?– egregJun 15, 2012 at 14:08 -
@egreg -- there are still a few "legacy" projects run on a vms system (e.g. annual reminders to members to update their membership information, uses tex because names and addresses contain accented letters, and the front end to the membership database is still on vms but probably not for more than another year), but book and journal production have been on unix/linux since about 2000. (production systems change slowly.) it's the only non-extended tex i have easily accessible, so took advantage of it for testing/wasting time. i think e-tex was made the default in tex live in the mid-2000s Jun 15, 2012 at 15:03
Another short way of making TeX blow up is to have a file named +.tex consisting of
\input+
Then +.tex inputs itself, and TeX sadly stops with the error
! TeX capacity exceeded, sorry [text input levels=15].
answered Oct 22, 2011 at 3:25
Yet another way to crash the engine: \closeout18\bye causes a segmentation fault in pdfTeX and in XeTeX when trying to ship out the page. The last line shown on the terminal is
[1zsh: segmentation fault (core dumped) pdftex '\closeout18\bye'
answered Jul 27, 2015 at 16:28
-
1I don't get any segmentation fault on my machine (TeX Live 2015,
x86_64-darwin)– egregJul 27, 2015 at 18:32 -
@egreg I still get a segfault with TeX Live 2015
i386-linux(I had tested that with TeX Live 2014). Aug 5, 2015 at 22:45 -
1Yes, I get it too with a Linux box (TL 2014), but it seems implementation dependent: a bug, rather than a feature.– egregAug 6, 2015 at 8:38
. so here's the challenge: produce shorter code that results inemergency stop` with knuth's original tex engine. no prizes, just glory. (and see my comments on the answers.)