Dollar signs in an edef yield tex capacity exceeded

Question

I want my two dollars:

\documentclass{minimal}
\begin{document}
\edef\twodollars{\$2}
\end{document}

However, all I get is:

! TeX capacity exceeded, sorry [input stack size=5000].
\font@name ->
             \OT1/cmr/m/n/10 
l.3 \edef\twodollars{\$
                       2}

Is it possible to use \edef with a value that includes a dollar sign?

Answer 1

Use

\documentclass{minimal}
\begin{document}
\edef\twodollars{\string$2} \twodollars
\end{document}

\string changes the category code for $ to 12 (other).

Answer 2

The correct way is to say

\makeatletter
\protected@edef\twodollars{\$2}
\makeatother

as \$ is defined via \DeclareRobustCommand. An alternative is to say

\usepackage{etoolbox}
\robustify\$
\edef\twodollars{\$2}