To install xapian-bindings-ruby21, run the following command in macOS terminal (Applications->Utilities->Terminal)
sudo port install xapian-bindings-ruby21
To see what files were installed by xapian-bindings-ruby21, run:
port contents xapian-bindings-ruby21
To later upgrade xapian-bindings-ruby21, run:
sudo port selfupdate && sudo port upgrade xapian-bindings-ruby21
Reporting an issue on MacPorts Trac
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Though anyone may search Trac for tickets, you must have a GitHub account in order to login to Trac to create tickets.