Comments about ${!a}

core/word_eval.py

@@ -435,6 +435,12 @@ def _ApplyPrefixOp(self, val, op_id):
        length = len(val.strs)
      return runtime.Str(str(length))
    elif op_id == Id.VSub_Bang:
      # NOTES:
      # - Could translate to eval('$' + name) or eval("\$$name")
      # - ${!array[@]} means something completely different.  TODO: implement that.
      # - It might make sense to suggest implementing this with associative
      #   arrays?

      # Treat the value of the variable as a variable name.
      return self.mem.GetVar(val.s)
    else: