\
ifpdf
,
\
ifxetex
and
\
ifluatex
.
\
ifthenelse
\char‘{
\
boolean{pdf}
\char‘}\char‘{<if pdf>\char‘}\char‘{<not pdf>\char‘}
The ifxetex package also provides a command
\
RequireXeTeX
which creates an error if the code is not running
under XeTeX; while the other packages don’t provide such a command,
it’s not really difficult to write one for yourself.
Now for those who want to do the job for themselves: here’s a
discussion of doing the job for PDFTeX and \
ifpdf
— the
eager programmer can regenerate \
ifxetex
or \
ifluatex
in the
same fashion. It’s not recommended\dots
Suppose you need to test whether your output will be PDF or
DVI. The natural thing is to check whether you have access to
some PDFTeX-only primitive; a good one to try (not least because it
was present in the very first releases of PDFTeX) is
\
pdfoutput
. So you try
\ifx\pdfoutput\undefined ... % not running PDFTeX \else ... % running PDFTeX \fi
Except that neither branch of this conditional is rock-solid. The first branch can be misleading, since the “awkward” user could have written:
\let\pdfoutput\undefined
so that your test will falsely choose the first alternative. While this is a theoretical problem, it is unlikely to be a major one.
More important is the user who loads a package that uses LaTeX-style testing for the command name’s existence (for example, the LaTeX graphics package, which is useful even to the Plain TeX user). Such a package may have gone ahead of you, so the test may need to be elaborated:\ifx\pdfoutput\undefined ... % not running PDFTeX \else \ifx\pdfoutput\relax ... % not running PDFTeX \else ... % running PDFTeX \fi \fi
If you only want to know whether some PDFTeX extension (such as marginal kerning) is present, you can stop at this point: you know as much as you need.
However, if you need to know whether you’re creating PDF output, you also need to know about the value of\
pdfoutput
:
\ifx\pdfoutput\undefined ... % not running PDFTeX \else \ifx\pdfoutput\relax ... % not running PDFTeX \else % running PDFTeX, with... \ifnum\pdfoutput>0 ... % PDF output \else ... % DVI output \fi \fi \fi
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=whatengine