R_STARTUP_INIT: Code string evaluated during the R startup process

[HenrikBengtsson]

Background

It is not possible to evaluate an R expression from the CLI prior to the first R prompt. For example, the following will evaluate the R expression, but then terminate R:

$ R --quiet -e 'message("hello")' 
> message("hello")
hello
> 
> 

Idea

With startup::startup() in ~/.Rprofile, we could support something like:

$ R_STARTUP_INIT='message("hello")' R --quiet
hello

> 1 + 2
[1] 3

>

To be decided: Should this be evaluated at the beginning or the end of the startup process? By doing it at the end, the expression can rely on user's custom setup to be in place.

[HenrikBengtsson]

Added

$ R_STARTUP_INIT='message("Current time: ", Sys.time())' R --quiet
Current time: 2019-03-28 13:58:53
>