CODE EXAMPLE FOR SHELL

Examples of add-apt-repository and updating the APT cache

# Adds a repository into the file
add-apt-repository 'deb http://us.archive.ubuntu.com/ubuntu xenial main universe' 

# Removes a repository from the file
add-apt-repository -r 'deb http://us.archive.ubuntu.com/ubuntu xenial main universe'

# Updates the APT cache
apt-get update