write18

From ConTeXt wiki

When write18 is turned on, it means that it's possible to execute external programs in the middle of a TeX run. This is required to make some modules such as those for R, lilypond, gnuplot, ... etc. to work properly, but may impose a security leak if you would be running TeX on a server with untrusted sources of TeX files, so it's turned off by default.

1 How to turn on write18
- 1.1 Windows - MikTeX
- 1.2 Linux/Mac
2 How to check if write18 is turned on
3 See also

[edit] How to turn on write18

[edit] Windows - MikTeX

MikTeX 2.5/2.6

Each application now has it's own configuration file. To enable write18 run

initexmf --edit-config-file=miktex\config\pdftex.ini

or (if you have MikTeX 2.5 or a version of ConTeXt from 2006)

initexmf --edit-config-file=miktex\config\pdfetex.ini

and put

EnableWrite18=t

into it. An alternative is to se the environment variable MIKTEX_ENABLEWRITE18=t.

[edit] Linux/Mac

First try to figure out where your configuration file resides:

kpsewhich texmf.cnf

will should return you something like

/usr/local/teTeX/texmf.cnf

/usr/local/gwTeX/texmf.cnf

In that file you'll probably find a line reading

shell_escape = f

Change that "f" (false) to "t" (true) to enable it.

[edit] How to check if write18 is turned on

Sometimes while writings a module, one needs to check if write18 is enabled or now. There are different ways in which this can be done.

A new primitive in pdftex 1.30: \pdfshellescape is a read-only integer that is 1 if \write18 is enabled, 0 otherwise.
ConTeXt defines \systemcommandmode that is 2 if \write18 is enabled, 1 otherwise.
A primitive \ifeof18 that is true if \write18 is disabled, false otherwise.