Detect which TeX engine is used

Question

How can I detect inside a TeX file which engine (pdftex/xetex/luatex) is used to compile the file? Is there a LaTeX package that provides this functionality?

Answer 1

Yes, there is — iftex. There are also ifxetex and ifluatex packages.

Internally these packages rely on checking if engine-specific primitives exist, such as \XeTeXversion.

Answer 2

Packages ifxetex, ifluatex, ifpdf. You can also look e.g. in hyperref to check how it detect which driver it should use.

Answer 3

I am using the following code:

%% ================================================================== 
%% 
%% Macros specific for latex / pdflatex / xetex compilers 
%% 
\usepackage{ifpdf,ifxetex,ifluatex} 
\ifpdf
    \typeout{^^J *** PDF mode *** } 
\else
    \typeout{^^J *** DVI mode ***} 
\fi 
\ifluatex
    \typeout{ *** LuaLaTeX *** ^^J}
    % patch \typein
    % see http://tex.stackexchange.com/questions/12435/incompatibilities-between-lualatex-and-typein
    \makeatletter
    \def\@xtypein[#1]#2{%
        \typeout{#2}%
        \@tempcnta\endlinechar
        \endlinechar\m@ne
        \read\@inputcheck to#1%
        \endlinechar\@tempcnta
        \@typein}
    \makeatother 
    % LuaLaTeX specific code
\else\ifxetex
    \typeout{ *** XeLaTeX *** ^^J} 
    % XeLaTeX specific code
\else
    \typeout{ *** LaTeX *** ^^J} 
\fi\fi 
\typein{} % pause to watch result
%% =====================================================================

LuaLaTeX can run both in DVI and PDF modes.