I self-studied Greek long ago, and I found this Perfect Imperative. Now all the Greek grammars I looked at just throw it at you, expecting you to either completely ignore or downright not have what seems like a natural and inevitable reaction to me: «WTF DOES THIS MEAN?!?!?!». Seriously: Perfect usually means past, so how do I make an imperative referring to something past? So I'm wondering: what other languages have Imperative Perfect, and what is the meaning of this mood-tense combination, generally speaking and also in particular in Greek?
What I guessed was that, putting together imperative, a command, and perfect, a completed action of which we can see the result (an interpretation of perfect that probably comes from the English Present Perfect, which I have been told to be used for actions of which the result is presently visible, with the example my professor always makes being "I have written 20 letters"), the Greek Imperative Perfect was a command of which one thought they already knew the result, in some sense. For example, in the Gongyla poem by Sappho (see p. 47 here, older version here pp. 239-240, something close to my reconstruction here), I accepted the Perfect Imperative because a command was perfectly fitting with "κέλομαι", and the "known result" was described later on in the poem.
I asked about this on Greek SE, but it's still in commitment, and since I've recently opened a blog where I will sooner or later upload translations of a fragment by Sappho I reconstructed (in a way that is clearly wrong in the sense that all authoritative sources give another version that is incompatible with mine) to have an Imperative Perfect, and thus I will have to explain what I.P. means, presumably, I decided to ask here as well in a broader less language-specific fashion, also because of a mild curiosity about how common such a mood-tense combination is.