Multiple R Versions

The Building R and R Contribution Workflow tutorials use the simplest set up, working on a single copy of the R sources.

It can be helpful to work with multiple versions of R:

to compare your modifications with an unmodified copy, e.g. to compare speed or memory usage, or
to work on independent changes, so that each patch only contains the changes for one bug fix or new feature.

You can build multiple R versions in the same Codespaces environment.

First choose a name for the R version. This will be used to identify the version and to name the build/source directory. By default, we use the name r-devel and the environment variables BUILDDIR and TOP_SRCDIR are set to match.

For illustration, we will use r-devel-raw, which you might use to name a version of R that you never modify.
You can set the BUILDDIR and TOP_SRCDIR environment variables to match your chosen name using the set_build_r function:
- Open a terminal in the codespace.
- Run the set_build_r function with your chosen name as the argument, e.g.
```
set_build_r r-devel-raw
```
  The new values of the environment variables will be printed as confirmation:
```
BUILDDIR is now set to /workspaces/r-dev-env/build/r-devel-raw
TOP_SRCDIR is now set to /workspaces/r-dev-env/svn/r-devel-raw
```
If you have an unmodified build of R-devel using the default name of r-devel, you can simply copy the sources and the build to the new directories with rsync:
```
rsync -a "$(dirname "$BUILDDIR")/r-devel/"* $BUILDDIR
rsync -a "$(dirname "$TOP_SRCDIR")/r-devel/"* $TOP_SRCDIR
```
Otherwise you can follow the steps in the Building R tutorial to checkout the R sources and build R using the new source and build directories.

Once you have a build of R under the new build directory, you will see your chosen name in the choices when running the which_r script to select the version of R to run in new terminals, e.g.

which_r

Which version of R should be used in new R terminals?
  1. R 4.4.0 (release version built into this container)
  Additional R builds available:
    2. r-devel
    3. r-devel-raw
Enter the number corresponding to the selected version:

Note

BUILDDIR and TOP_SRCDIR will be set to the defaults using the label r-devel whenever a new bash terminal is opened, e.g. when the codespace is restarted.

Whenever following instructions that use these variables to refer to the build and source directory, be sure they are pointing to the desired version!

You can check the values any time with

echo $BUILDDIR
echo $TOP_SRCDIR

and switch with set_build_r <name>.