link

Transmits on a frequency, like a Redstone Link transmitter powered with that strength. Every receiver of the frequency within range outputs the strongest signal transmitted on it.

link.set("minecraft:iron_ingot", "minecraft:gold_ingot", 15)
link.set("red_dye", "blue_dye", true)   -- "minecraft:" is understood
link.set("red_dye", "blue_dye", false)  -- stop transmitting

As with rs.set, a strength above 15 becomes 15, below 0 becomes 0, and it must be a whole number. The errors you may meet:

The limit counts every frequency used since the computer booted, with link.set, link.get or a Redstone Link block driven as a peripheral (Redstone Link). It goes back to zero at the next reboot.

Doors across the base. The control room opens the warehouse doors, 120 blocks away. Next to the doors, a Redstone Link receiver holds an iron ingot and a gold ingot and powers them:

local DOORS = {"minecraft:iron_ingot", "minecraft:gold_ingot"}

while true do
  write("doors (open/close): ")
  local answer = read()
  if answer == "open" then
    link.set(DOORS[1], DOORS[2], true)
    print("opening")
  elseif answer == "close" then
    link.set(DOORS[1], DOORS[2], false)
    print("closing")
  end
end

A Mechanical Press line switched from afar. The press line stops when its Clutch is powered. A Redstone Link receiver (iron sheet + clutch) next to the Clutch powers it. Far away, a Comparator reads the input vault of the line and powers a Redstone Link transmitter (iron ingot + comparator). The computer runs the line only while there is iron to press, and wakes up on the link event (see link.get):

local LEVEL = {"minecraft:iron_ingot", "minecraft:comparator"}
local CLUTCH = {"create:iron_sheet", "create:clutch"}

local function update()
  local level = link.get(LEVEL[1], LEVEL[2])
  -- a powered Clutch disconnects: power it to stop the line
  link.set(CLUTCH[1], CLUTCH[2], level == 0)
  if level == 0 then
    print("input empty: line stopped")
  else
    print("input level " .. level .. ": pressing")
  end
end

update()
while true do
  os.pull_event("link")
  update()
end

See also link.get() rs.set()

Reads a frequency, like a Redstone Link receiver: the strongest signal transmitted on it by the other links in range (and other computers), 0 when nobody transmits. The computer's own transmission is never counted.

-- a Daylight Detector on the roof powers a transmitter (glowstone dust + clock)
local light = link.get("minecraft:glowstone_dust", "minecraft:clock")
print("daylight: " .. light .. "/15")

The item ids are checked as for link.set, with the same errors.

**The link event.** The first link.get or link.set on a frequency also starts listening to it. From then on, each time the strength received on it changes, the computer queues a link event with three fields:

Only the frequencies the program already used send it, so call link.get once on each frequency you want to hear. That first call returns what is already on the air: no event comes for it.

e.a and e.b are spelled the way the program first wrote them: after link.get("red_dye", "blue_dye"), the event says "red_dye", not "minecraft:red_dye". Compare with the same spelling. See also Events.

A wireless alarm network. Around the base, each detector (a pressure plate at the gate, a Sculk Sensor at the mine entrance, a tripwire on the pier) powers a Redstone Link transmitter that holds red dye and the item of its zone. The bells of the town hang on a receiver (red dye + bell). The computer listens to every zone, rings the bells while one of them is on, and names the zones on its screen:

local ZONES = {
  {name = "north gate", item = "minecraft:oak_door"},
  {name = "mine", item = "minecraft:iron_pickaxe"},
  {name = "harbour", item = "minecraft:oak_boat"},
}

for _, zone in ipairs(ZONES) do
  zone.power = link.get("minecraft:red_dye", zone.item)  -- listens from now on
end

local function refresh()
  local alarms = {}
  for _, zone in ipairs(ZONES) do
    if zone.power > 0 then
      table.insert(alarms, zone.name)
    end
  end
  link.set("minecraft:red_dye", "minecraft:bell", #alarms > 0)
  term.clear()
  term.set_cursor(1, 1)
  if #alarms == 0 then
    print("all quiet")
  else
    print("ALARM: " .. table.concat(alarms, ", "))
  end
end

refresh()
while true do
  local e = os.pull_event("link")
  for _, zone in ipairs(ZONES) do
    if e.a == "minecraft:red_dye" and e.b == zone.item then
      zone.power = e.power
    end
  end
  refresh()
end

See also link.set() os.pull_event()