[Linux] Add/remove PPA repositories

You can easily add and remove PPA repositories to your software sources with the apt-add-repository command. Use:

sudo apt-add-repository ppa:USER/REPOSITORY

to add and:

sudo apt-add-repository -r ppa:USER/REPOSITORY

to ONLY remove (same as --remove) it. Alternatively, if you installed ppa-purge, you can use it to remove the repository AND (if possible) revert to the official packages:

sudo ppa-purge ppa:USER/REPOSITORY