Using multiple R versions

Backup

tar -cvzf ~/Documents/R-backup.tgz $(ls -d /Library/Frameworks/R.framework/)

Backup Libraries

tar -cvzf ~/Documents/pkg-backup.tgz $(ls -d /Library/Frameworks/R.framework/Versions/[34]*/Resources/library)

https://rud.is/rswitch/

RSwitch

R for macOS DevelopersR for macOS Developers

R Installation and Administration

pkgutil --forget org.r-project.R.el-capitan.fw.pkg

https://mac.r-project.org/high-sierra/R-4.0-branch/x86_64/R-4.0-branch.tar.gz

https://mac.r-project.org/el-capitan/R-3.6-branch/R-GUI-7782-3.6-el-capitan-Release.dmg

https://mac.r-project.org/high-sierra/R-4.0-branch/R-GUI-7842-4.0-high-sierra-Release.dmg