s = "Ἐν ἀρχῇ ἐποίησεν ὁ θεὸς τὸν οὐρανὸν καὶ τὴν γῆν"

usubstr(s, 25, 11)
  τὸν οὐρανὸν

usubstr(s, 25, .)
  τὸν οὐρανὸν καὶ τὴν γῆν

usubstr(s, 1, ustrlen(s)-1)
  Ἐν ἀρχῇ ἐποίησεν ὁ θεὸς τὸν οὐρανὸν καὶ τὴν γῆ

usubstr(s, -3, .)
  γῆν