export variable from bash to R

Dear R experts

This probably seems very easy to you guys, but I'm a beginner and would be
really glad if someone helped me with this:
I am trying to automate the execution of an R script (let's call it
"myscript.R") by passing a variable from a bash script to myscript.R.
I know I can use the command Rscript, but I don't know how to declare in
bash which variable will be accessed by the "commandArgs" command in
myscript.R.

So my bash script looks about like this:

#!/bin/bash

VARIABLES=( a b c d )

for i in ${VARIABLES[@]}; do
        VARIABLENAME=$i
        Rscript -e 'source("myscript.R")'
done

In myscript.R, I would like to use the current VARIABLENAME when executing
the program, i.e.,
myscript <- function()  {

args <- commandArgs(TRUE)     # args should now be set to either a,b,c, or d
load(paste("/home/user/../../", args, ".RData", sep=""))    #  this defines
the path to the data file that will be used in this run

...further commands...
}

At the moment, myscript.R doesn't seem to be executed at all when I execute
the bash script.
Any help will be greatly appreciated!