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.

score 22 · Accepted Answer · answered Sep 21 '12 at 15:03

22

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)

answered Sep 21 '12 at 15:03

David Robinson

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score 6 · Answer 2 · answered Sep 21 '12 at 15:22

6

Try this:

.Internal(Sys.setenv(var.name, var.value))

answered Sep 21 '12 at 15:22

G. Grothendieck

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2

+1 but don't do this in a package, as it's against CRAN policies. – Joshua Ulrich Sep 21 '12 at 17:52
@JoshuaUlrich, can you please elaborate on your comment? Is it because `.Internal` functions are not subject to the same (strict) backward compatibility requirements? – flodel Sep 21 '12 at 17:55
3

@flodel: see the [CRAN Repository Policy](http://cran.r-project.org/web/packages/policies.html): "CRAN packages should use only the public API..." – Joshua Ulrich Sep 21 '12 at 17:57

score 1 · Answer 3 · answered Jul 31 '20 at 18:55

This is a variant of the accepted answer, but if you want to pack this into a single line, and/or avoid generating the intermediate args object, you can use setNames to get a named character vector, then coerce to list with as.list:

do.call(Sys.setenv, as.list(setNames(var.value, var.name)))

setting environment variables programmatically

3 Answers3

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