If you previously used either the clang4, clang6, clang7, gfortran 6.1, or the macos-rtools installer, please consider deleting the old components that were installed. Note: Special care should be taken when removing files with the rm command. Make sure the commands and file paths are copied in verbatim to a text editor and, then, run in Terminal. To do so, open the Terminal from /Applications/Utilities/ and type:

Delete the clang4,6,7 binary sudo rm -rf /usr/local/clang{4,6,7} # Delete the prior version of gfortran installed sudo rm -rf /usr/local/gfortran sudo rm -rf /usr/local/bin/gfortra …