Deriving base port/package names

[Ronald F. Guilmette]

Given a list of all current FreeBSD ports/package, such as a (plain text
version) the list found here:

   https://www.freebsd.org/ports/master-index.html

and assuming that all text past the ' -- ' has already been deleted
from each line, what would be a proper sort of sed command to extract
_just_ the port/package names, without the version numbers attached?