General ⇒ Add text to a variable

[jj2]

Hi,

How do i add text to a variable which i defined earlier in the document? I tried it like this:

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\def\exos{some text}
\def\variable{\exos}
\def\exos{\variable added text}

but that doesn't work.

[cgnieder]

Hi and welcome to the LaTeX community.

Strictly speaking there are no variables in TeX. There are two kinds of control sequences: TeX primitives and macros. Those macros can either have parameters or be parameter-less. The last type, a parameter-less macro, is the closest thing to a variable.

This means adding something to a macro is redefining the macro in a way that it contains the previous definition (i.e. the once expanded macro). Here is a plain e-TeX way:

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\def\pretovar#1#2{\edef#1{\unexpanded{#2}\unexpanded\expandafter{#1}}}
\def\addtovar#1#2{\edef#1{\unexpanded\expandafter{#1#2}}}

\tt
\def\variable{var}
\meaning\variable

\pretovar\variable{pre}
\meaning\variable

\addtovar\variable{post}
\meaning\variable

\bye

If you're using LaTeX you can use ready-made macros for this by loading the etoolbox package:

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\documentclass{article}
\usepackage{etoolbox}
\begin{document}

\ttfamily
\def\variable{var}
\meaning\variable

\preto\variable{pre}
\meaning\variable

\appto\variable{post}
\meaning\variable

\end{document}

Regards