The package provides the switch \ifetex which indicates whether e-TeX is available or not.

The package can be loaded as LaTeX package using \usepackage{ifetex} or in plain TeX using \input ifetex. In either case it aborts silently if the \ifetex macro is already defined.

The package’s test is whether \eTeXversion is defined as a primitive; if it is, the package assumes e-TeX features are available.

The author is Martin Scharrer. The package is Copyright © 2011 Martin Scharrer.