[texhax] tikz externalize with LuaTeX 0.95

David Carlisle d.p.carlisle at gmail.com
Tue May 31 17:50:45 CEST 2016

On 31 May 2016 at 15:46, Arno Trautmann <Arno.Trautmann at gmx.de> wrote:

> I cannot quite grasp the concept of this right now, but thank you very
> much for the quick response!
> Best,
> Arno

classic tex (and etex and xetex and luatex until last year) has 16 write

Normally writing to a number >15 isn't an error but just writes to the log.
However web2c tex treats write18 as a hook to call system commands.

recent luatex releases increase the number of write streams to 256 and drop
the special nature of write18: it becomes a normal stream like write17 or

the shellesc package (which we added to latex/tools earlier this year)
defines \write in luatex to check for 18 and if so to use Lua
\directlua{os.exec... to call the system command so gets things back on

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