[Rd] maintaining multiple R versions

[Paul Gilbert]

(somewhat related to thread [Rd] R CMD check not reading R_LIBS )

For many years I have maintained R versions by building R (./configure ; 
make)  in a directory indicating the version number, putting the 
directory/bin on my path, and setting R_LIBS_SITE.

It seems only one version can easily be installing in /usr/bin, and in 
any case that requires root, so I do not do that. There may be an 
advantage to installing somewhere in a directory with the version 
number, but that does not remove the need to set my path. (If there is 
an advantage to installing I would appreciate someone explaining briefly 
what it is.)

My main question is whether there is a better ways to maintaining 
multiple versions, in some way that lets users choose which one they are 
using?

(The only problem I am aware of with my current way of doing this is:
if the system has some R in /usr/bin then I have to set my preferred 
version first, which means shell commands like "man" find R's pager 
first, and do not work.)

Thanks,
Paul