Variables in LaTeX using komascript.

urgh.tex

\documentclass{article}

\usepackage{xspace}
% The Magic Sauce.

\usepackage{scrletter}

\makeatletter
\newkomavar[urghhh]{documentTitle}
\setkomavar{documentTitle}{\@title}

\newkomavar[urgh]{documentSubTitle}
\setkomavar{documentSubTitle}{}

\newcommand{\subtitle}[1]{\setkomavar{documentSubTitle}{#1}}

\newcommand{\theTitle}{\usekomavar{documentTitle}}
\newcommand{\theSubtitle}{\usekomavar{documentSubTitle}}

\newcommand{\theFullTitle}{%
  \theTitle%
  \ifkomavarempty{documentSubTitle}
    {}
    {:\xspace\theSubtitle}}
  \makeatother

\title{Foo}
\subtitle{Bar}

\begin{document}

\begin{enumerate}
\item\theTitle{}

\item \theSubtitle{}

\item \theFullTitle{}

\end{enumerate}

\subtitle{}

\begin{enumerate}
\item \theTitle{}

\item \theSubtitle{}

\item \theFullTitle{}

\end{enumerate}

\end{document}
%%% Local Variables:
%%% mode: latex
%%% TeX-master: t
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