Using string variable with LaTeX

Question

I would like to define one variable containing some text that can be changed locally. The following code gives one example of the featuring I'm looking for.

\documentclass{article}
    \newcommand{\someSpecialText}{A text that can be changed locally...}
    \newcommand{\testIt}{The value of someSpecialText is : ''\someSpecialText''.}

\begin{document}

% The default behavior.
\testIt

% Here I would like to change the definition of `\someSpecialText`
% or anywhere else in the document.
\testIt

\end{document}

Answer 1

You can use a standard \renewcommand to modify the text:

\documentclass{article}
\newcommand{\someSpecialText}{A text that can be changed locally\ldots}
\newcommand{\testIt}{The value of \texttt{someSpecialText} is : ``\someSpecialText''.}

\begin{document}

% The default behavior.
\testIt

% Here I would like to change the definition of `\someSpecialText`
% or anywhere else in the document.
{% Start of group
\renewcommand{\someSpecialText}{A text that \textit{was} changed locally\ldots}
\testIt
}% End of group

% The default behavior.
\testIt

\end{document}​

In the above example, the \renewcommand was placed inside a group, defined by the braces { and } to localize the redefinition. If this behaviour is not desired, simply remove the braces to make the redefinition global from that point forward.

---

Of course, one can also write this in a macro form, which could be considered "shorter", with some default value. Here is an example:

\documentclass{article}
\newcommand{\testIt}[1][A text that can be changed locally\ldots]{The value passed to \texttt{testIt} is : ``#1''.}

\begin{document}

% The default behavior.
\testIt

% Here I would like to change the definition of `\someSpecialText`
% or anywhere else in the document.
\testIt[A text that \textit{was} changed locally\ldots]

% The default behavior.
\testIt

\end{document}​

\testIt is set up to output something with a default value. However, you can supply an optional argument that modifies the default behaviour.