Question about eval in PHP 5

Question

I have been doing PHP stuff for almost one year and I have never used the function eval() though I know the usage of it. But I found many questions about it in

Answer 1

Well I have used eval once. This was for a system, where the users could enter formulas using constants fished from the underlying system.

A string like:

(N * (G - 2,7)) / E

was taken and the constants replaced with values from the system eval is then used to get a value. eval seemed like the easiest way to go. The statement was filtered to only allow operators and uppercase letters(no two next to each other) so perhaps this is not a "real" use case of eval, but it works and is pretty readable.

That said the system in questing is huge (200k+ lines) and this is the only place that eval is used.