This is a docker container that builds and uses the arduino toolchain directly, without using the Arduino IDE.
To create the image, run docker build -t arduino .. There is an optional --build-arg of TOOLCHAIN_ARCHIVE so that you may point to a fork or branch, it defaults to https://github.com/arduino/toolchain-avr/archive/master.zip.
To get the results of the build you could do something like docker run -v /tmp/avr:/tohost arduino cp -r /objdir/bin /tohost.
If you want to just use the binaries in the container, try docker run arduino avr-cpp --help. Maybe you'd like to alias dra=docker run arduino or similar.