The apt-add-repository
manpage says this about the command:
REPOSITORY can be either a line that can be added directly to
sources.list(5), in the form ppa:<user>/<ppa-name> for adding Personal
Package Archives, or a distribution component to enable.
In the first form, REPOSITORY will just be appended to
/etc/apt/sources.list.
In the second form, ppa:<user>/<ppa-name> will be expanded to the full
deb line of the PPA and added into a new file in the
/etc/apt/sources.list.d/ directory. The GPG public key of the newly
added PPA will also be downloaded and added to apt's keyring.
In the third form, the given distribution component will be enabled for
all sources.
and:
-r, --remove Remove the specified repository
So add-apt-repository
just adds and removes lines from /etc/apt/sources.list
and /etc/apt/sources.list.d/
.
The ppa-purge
manpage says this:
NAME
ppa-purge - disables a PPA and reverts to official packages
DESCRIPTION
This script provides a bash shell script capable of automatically
downgrading all packages in a given PPA back to the ubuntu versions.
You have to run it using root privileges because of the package
manager.
So ppa-purge
will not only remove a PPA, it will also downgrade any packages back to their default versions. This is useful when testing beta or newer versions of software.