How is to add R and Rtools paths in the environment variable?

Question

I have installed R-3.5.1 and Rtools35.exe . But I am unable to install packages in R . Somewhere I got,

Make sure the R and Rtools paths are added in the environment variable.

But I don't know what is environment variable and how is to add R and Rtools paths in the environment variable?

Edit

The answer provided How to add Rtools\\bin to the system path in R requires library(devtools) . But install.packages("devtools") isn't working.

Answer 1

Installing package that has heavy dependencies just to set environment variables doesn't seem to be good solution.

Below solution is for R 4.0.0 and rtools40.

This uses powershell bash, it should be available on all recent Windows versions.

$ENV:PATH = "C:\R\bin;C:\rtools40\usr\bin;$ENV:PATH"

You can see full R 4.0.0 setup on Windows in this CI yaml .

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Note that in powershell it is best to refer to applications using .exe suffix, because powershell has many aliases, so using R or curl will not do what you expect, you need R.exe or curl.exe instead.