LSJ

εὖγε or εὖ γε , Adv.
A. well, rightly, in replies confirming or approving what has been said: as σοὶ γὰρ χαρίζομαι. Answ. “εὖγε σὺ ποιῶν” Pl. R.351c; “εὖγ᾽, εὖγε ποιήσαντες” Ar.Pax285; “εὖγε, εὖγε, ὦ κύνες, ἕπεσθε” X.Cyn.6.19: iron., “εὖ γοῦν θίγοις ἂν χερνίβων” E.Or.1602; “εὖγε μέντἂν διετέθην” Ar.Av.1692.
2. without a Verb, good! well said! well done! Pl.Grg.494c, al.; doubled “εὖγ᾽, εὖγε” Ar.Eq.470; εὖγ᾽, “εὖγε, νὴ Δἴ, εὖγε” Id.Ec.213; “εὖγ᾽, ὅτι ἐπείσθης” Id.Nu.866: c. gen., “εὖγε τῆς προαιρέσεως” Luc.Vit.Auct.8.

http://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0057:alphabetic+letter%3D*e:entry+group%3D274:entry%3Deu)%3Dge