How to get linux to recognize where R is located - r

Question

I am sure this is a trivial question, but I am trying to install multiple R versions in Linux. I am not using R studio server pro and am instead using the free R studio server. I followed this documentation to install R but got errors when I attempted to locate it. However, when I run a command to see what version of R is installed, there is no error.
R is installed!
(base) noah#noah-VirtualBox:/opt/R/4.1.3$ /opt/R/4.1.3/bin/R --version
R version 4.1.3 (2022-03-10) -- "One Push-Up"
Copyright (C) 2022 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)
R is free software and comes with ABSOLUTELY NO WARRANTY.
You are welcome to redistribute it under the terms of the
GNU General Public License versions 2 or 3.
For more information about these matters see
https://www.gnu.org/licenses/.
Attempts
(base) noah#noah-VirtualBox:/opt/R/4.1.3$ R
Command 'R' not found, but can be installed with:
sudo apt install r-base-core
(base) noah#noah-VirtualBox:/opt/R/4.1.3$ which R
(base) noah#noah-VirtualBox:/opt/R/4.1.3$
Steps to reproduce
export R_VERSION=4.1.3
curl -O https://cran.rstudio.com/src/base/R-4/R-${R_VERSION}.tar.gz
tar -xzvf R-${R_VERSION}.tar.gz
cd R-${R_VERSION}
# Build and install R
./configure \
--prefix=/opt/R/${R_VERSION} \
--enable-memory-profiling \
--enable-R-shlib \
--with-blas \
--with-lapack
make
sudo make install
# Verify R installation
/opt/R/${R_VERSION}/bin/R --version
# Create a symlink to R
sudo ln -s /opt/R/${R_VERSION}/bin/R /usr/local/bin/R
sudo ln -s /opt/R/${R_VERSION}/bin/Rscript /usr/local/bin/Rscript
# Export path so Rstudio can find it
export RSTUDIO_WHICH_R='/opt/R/4.1.3/bin'

Answer 1

You are overcomplicating it. Just install in, say,
/opt/R/4.2.0/
/opt/R/4.1.2/
/opt/R/4.0.5/
and then either set the $PATH to the bin/ directory in the version you want, or call R directly. It is what pretty much exactly what many of us have done with two versions of R (i.e. R-release and R-devel):
$ R --version | head -1
R version 4.2.0 (2022-04-22) -- "Vigorous Calisthenics"
$
$ /usr/lib/R/bin/R --version | head -1
R version 4.2.0 (2022-04-22) -- "Vigorous Calisthenics"
$
$ /usr/local/lib/R-devel/bin/R --version | head -1
R Under development (unstable) (2022-05-24 r82398) -- "Unsuffered Consequences"
$
The first two are the same as that is my 'default' version. The third is my one alternate. And that is all there is to it.

Answer 2

If you add /usr/local/bin to your $PATH variable you would have been able to launch R, if it was not already present.
You could add it to .bashrc in your home directory
echo "export path=\"${PATH}:/usr/local/bin\"" |tee -a ~/.bashrc
Links for installing R from package, Ubuntu / Debian, RHEL 9, RHEL 8, RHEL/CentOS7
https://docs.posit.co/resources/install-r/
Also see
(Optional) Install multiple versions of R, on the same page.