setting environment variables programmatically

Question

In R, I can set environment variables "manually", for example:

Sys.setenv(TODAY = "Friday")

But what if the environment variable name and value are stored in R objects?

var.name  <- "TODAY"
var.value <- "Friday"

I wrote this:

expr <- paste("Sys.setenv(", var.name, " = '", var.value, "')", sep = "")
expr
# [1] "Sys.setenv(TODAY = 'Friday')"
eval(parse(text = expr))

which does work:

Sys.getenv("TODAY")
# 1] "Friday"

but I find it quite ugly. Is there a better way? Thank you.

Answer 1

You can use do.call to call the function with that named argument:

args = list(var.value)
names(args) = var.name
do.call(Sys.setenv, args)