valid_packages = list_packages () returns an Nx2 cell array naming every package at Octave Packages that is installable with the pkg command, against the URL of its latest release. A package qualifies by declaring pkg among the dependencies of that release. The index is fetched from Octave Packages, and a fetch that does not succeed is an error saying so.

valid_packages = list_packages (index) reads the index from index instead of fetching it, given either as the JSON text or as the structure jsondecode returns for it. This is what makes the selection testable without reaching the network, and it is useful against a copy of the index taken earlier.

An index in which nothing qualifies returns an empty cell array rather than nothing at all.

Source Code: list_packages