Install Homebrew. You may (probably) already have Homebrew installed on your Mac, but if not, you should install it now. Here is the command to install it:

# install homebrew
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

Next, use Homebrew to install bash-completion. Here is the command:

# use homebrew to install bash completion 
brew install bash-completion

The installation of bash-completion will instruct you to add the following line to your ~/.bash_profile file:

# update the bash profile to enable bash completion for every terminal session 
[ -f /usr/local/etc/bash_completion ] && . /usr/local/etc/bash_completion

Now, create the links necessary to enable the Docker command-line completion feature. There is one link for each of the Docker toolsets. Here are the link commands for bash (if you use zsh, check the next code block for the link commands):

# create links for bash shell
ln -s /Applications/Docker.app/Contents/Resources/etc/docker.bash-completion $(brew --prefix)/etc/bash_completion.d/docker
ln -s /Applications/Docker.app/Contents/Resources/etc/docker-machine.bash-completion $(brew --prefix)/etc/bash_completion.d/docker-machine
ln -s /Applications/Docker.app/Contents/Resources/etc/docker-compose.bash-completion $(brew --prefix)/etc/bash_completion.d/docker-compose

Note that if you are using zsh instead of bash, the link commands are different. Here are the link commands for zsh:

# create links for zsh shell
ln -s /Applications/Docker.app/Contents/Resources/etc/docker.zsh-completion /usr/local/share/zsh/site-functions/_docker
ln -s /Applications/Docker.app/Contents/Resources/etc/docker-machine.zsh-completion /usr/local/share/zsh/site-functions/_docker-machine
ln -s /Applications/Docker.app/Contents/Resources/etc/docker-compose.zsh-completion /usr/local/share/zsh/site-functions/_docker-compose

Finally, restart your terminal session—you can now use Docker command completion! Try it by typing docker and hitting the Tab key twice.