dist.lua

local function getFaceTo()
  local pos0 = vector.new(gps.locate())
  turtle.forward()
  local pos1 = vector.new(gps.locate())
  local dist = pos1 - pos0
  turtle.back()
  local faceto = ""
  if dist.x > 0 then
    faceto = "west"
  elseif dist.x < 0 then
    faceto = "east"
  elseif dist.z > 0 then
    faceto = "north"
  else
    faceto = "south"
  end
  return faceto
end

local function forback(dist)
  d = dist
  if d < 0 then
    d = -d
  end
  if dist > 0 then
    print("forward:"..tostring(d))
  else
    print("back:"..tostring(d))
  end
end

local function dispStatus(pos, target, faceto)
  print("pos:"..tostring(pos))
  print("faceTo:"..faceto)
  print("dist:"..tostring(target - pos))
end

args = {...}
x = tonumber(args[1])
y = tonumber(args[2])
z = tonumber(args[3])
target = vector.new(x, y, z)

rednet.open("left")
curpos = vector.new(gps.locate())

faceto = getFaceTo()
dispStatus(curpos, target, faceto)
dist = target - curpos
forback(dist.z)