Build an image from a Dockerfile.

# To build a docker image using the Dockerfile in the current directory:
docker build .

# To build a docker image from a Dockerfile at a specified URL:
docker build <github.com/creack/docker-firefox>

# To build a docker image and tag it:
docker build --tag <name:tag> .

# To not use the cache when building the image:
docker build --no-cache --tag <name:tag> .

# To build a docker image using a specific Dockerfile:
docker build --file <Dockerfile> .

# To build with custom build-time variables:
docker build --build-arg <HTTP_PROXY=http://10.20.30.2:1234> --build-arg <FTP_PROXY=http://40.50.60.5:4567> .