Tiffany B. Brown

While attempting to install Fabric for a project, I ran into the following error message (straight from my pip.log).

clang: error: unknown argument: '-mno-fused-madd' [-Wunused-command-line-argument-hard-error-in-future]

clang: note: this will be a hard error (cannot be downgraded to a warning) in the future

error: command 'cc' failed with exit status 1

Some Googling revealed that this is an issue with the XCode 5.1 update. This update treats unrecognized command-line options as errors. And has been causing a lot of facepalming for users of Ruby gems and Python libraries. The fix is a simple one. Just open up Terminal and type:

export CFLAGS=-Qunused-arguments
export CPPFLAGS=-Qunused-arguments

Then run pip install [package name] as usual. If you need to use sudo to install packages with pip, use sudo -E instead:

sudo -E pip install fabric

Source.