% switches.
\newif\ifphoto % show photo.
\newif\ifextra % show extra content.
\newif\ifen    % english language.
\newif\ifru    % russian language.
\newcommand{\en}[1]{\ifen#1\fi} % print if english language.
\newcommand{\ru}[1]{\ifru#1\fi} % print if russian language.

% read env variables.
\def\envtrue{true}   % true.
\def\envfalse{false} % false.
\def\enven{en}       % english literal.
\def\envru{ru}       % russian literal.
\def\envempty{}      % empty env value.
\getenv[\envphoto]{DOCUMENT_PHOTO} % read photo shell variable.
\getenv[\envextra]{DOCUMENT_EXTRA} % read extra shell variable.
\getenv[\envlang]{DOCUMENT_LANG}   % read language shell variable.
\ifdefequal{\envphoto}{\envtrue}{\phototrue}{\photofalse} % show photo.
\ifdefequal{\envextra}{\envtrue}{\extratrue}{\extrafalse} % show extra content.
\ifdefequal{\envlang}{\enven}{\entrue}{}                  % use english.
\ifdefequal{\envlang}{\envru}{\rutrue}{}                  % use russian.
\ifdefequal{\envlang}{\envempty}{\entrue}{}               % use english by default.
