Here is my Plain Tex file (example taken from the manual)

\input tikz.tex




We are working on


\draw (-1.5,0) -- (1.5,0);

\draw (0,-1.5) -- (0,1.5);



Here it is the log, when I try to compile using tex (pdftex works fine)

This is TeX, Version 3.14159265 (TeX Live 2020/Debian) (preloaded format=tex 2020.10.11)  24 OCT 2020 22:32

! Undefined control sequence.
\pgfutil@IfUndefined #1->\ifcsname 
                                   #1\endcsname \expandafter \pgfutil@second...
l.849 \pgfutil@IfUndefined{directlua}
? X
No pages of output.

1 Answer 1


\ifcsname is an extended command not available in the original TeX, so use the command etex if you want dvi or pdftex if you want PDF.

The start of the terminal output should look like

$ etex file
This is pdfTeX, Version 3.14159265-2.6-1.40.21 (TeX Live 2020) (preloaded format=etex)
 restricted \write18 enabled.
entering extended mode

Note the entering extended mode

  • . . . or luatex
    – DG'
    Commented Oct 24, 2020 at 20:58
  • 1
    @DG' or xetex or ptex yes, basically anything except "tex" :-) Commented Oct 24, 2020 at 20:59

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