Original Question

This seems easy and has likely been asked before, but I could not find it via a search.

I have a few flavors of R installed. I simply want to know, when I run RStudio, which flavor of R is it pointing to. So, I need a command -- within RStudio itself, ideally -- that can tell me the underlying R executable that is being used for this RStudio window that I am currently working with.

To be clear, I do not need / want to know the version of R that I'm using (e.g., R version 3.2.2 (2015-08-14) -- 'Fire Safety'). Instead, I want to know the actual path that RStudio is using to get to R -- looking at it from within RStudio -- so that I know "for reals" which version it's using. (E.g., /usr/local/bin/R.)

Edit & Answer

There are a lot of great discussions here, and some are OS-specific. I have a Mac. In my case, I found that:

> system("type R")
R is /usr/local/bin/R

> R.home()
[1] "/usr/local/Cellar/r/3.2.2_1/"

> file.path(R.home("bin"), "R")
[1] "/usr/local/Cellar/r/3.2.2_1/"

As those of you familiar can see, I am using brew. If I look for /usr/local/bin/R outside of R, I see:

$ ls -l /usr/local/bin/R
lrwxr-xr-x  1 mike  admin  25 Nov 14 17:31 /usr/local/bin/R -> ../Cellar/r/3.2.2_1/bin/R

which eventually resolves (2 symbolic links) to:

/usr/local/Cellar/r/3.2.2_1/

as the final destination.

So on my system (Mac OS X), file.path(R.home("bin"), "R") was the most accurate.