Examining contents of .rdata file by attaching into a new environment - possible?

Question

I am interested in listing objects in an RDATA file and loading only selected objects, rather than the whole set (in case some may be big or may already exist in the environment

Answer 1

I just use an env= argument to load():

> x <- 1; y <- 2; z <- "foo"
> save(x, y, z, file="/tmp/foo.RData")
> ne <- new.env()
> load(file="/tmp/foo.RData", env=ne)
> ls(env=ne)
[1] "x" "y" "z"
> ne$z
[1] "foo"
> 

The cost of this approach is that you do read the whole RData file---but on the other hand that seems to be unavoidable anyway as no other method seems to offer a list of the 'content' of such a file.