/usr/share/texlive/texmf-dist/tex/plain/graphics-pln/picture.tex is in texlive-plain-extra 2014.20141024-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 | % Plain TeX interface to picture mode.
% David Carlisle
\input miniltx
\makeatletter
\let\@@line\line
\input autopict.sty
\let\LaTeX@line\line
\let\line\@@line
\newdimen\@wholewidth
\newdimen\@halfwidth
\newdimen\unitlength \unitlength =1pt
\newbox\@picbox
\newdimen\@picht
\newcount\@xarg
\newcount\@yarg
\newcount\@yyarg
\font\tenln =line10 \font\tenlnw =linew10\relax
\font\tencirc=lcircle10 \font\tencircw=lcirclew10\relax
\newcount\@multicnt
\newdimen\@xdim
\newdimen\@ydim
\newbox\@linechar
\newdimen\@linelen
\newdimen\@clnwd
\newdimen\@clnht
\newdimen\@dashdim
\newbox\@dashbox
\newcount\@dashcnt
\let\@linefnt\tenln
\let\@circlefnt\tencirc
\@wholewidth\fontdimen8\tenln
\@halfwidth .5\@wholewidth
\def\picture#1{%
\begingroup
\let\line\LaTeX@line
\def\end##1{\csname end##1\endcsname}%
\pictur@#1}
\let\@@endpicture\endpicture
\def\endpicture{\@@endpicture\endgroup}
\def\LaTeXbegin{\def\begin##1{\csname##1\endcsname}}
\resetatcatcode
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