If you're using [homebrew,](http://brew.sh/) you can use the following commands:
brew tap osx-cross/avr
- brew install avr-libc
+ brew tap PX4/homebrew-px4
+ brew update
+ brew install avr-gcc
brew install dfu-programmer
+ brew install gcc-arm-none-eabi
This is the recommended method. If you don't have homebrew, [install it!](http://brew.sh/) It's very much worth it for anyone who works in the command line. Note that the `make` and `make install` portion during the homebrew installation of avr-libc can take over 20 minutes and exhibit high CPU usage.