i tried to find a built-in for geometric mean but couldn't.

(Obviously a built-in isn't going to save me any time while working in the shell, nor do i suspect there's any difference in accuracy; for scripts i try to use built-ins as often as possible, where the (cumulative) performance gain is often noticeable.

In case there isn't one (which i doubt is the case) here's mine.

gm_mean = function(a){prod(a)^(1/length(a))}