Halliday & Matthiessen (2014: 196):
Greetings include salutations, e.g. Hullo!, Good morning!, Welcome!, Hi!, and valedictions, such as Goodbye!, See you!; together with their responses, largely the same set of forms. Under this heading we could include well-wishings, like Your very good health!, Cheers!, Good shot!, Congratulations!. Both calls and greetings include some that are structured as clauses or nominal groups.Cf. The Lord be with you, God forgive you your sins and God bless you.