Cheat sheet

-- a comment to the end of the line
--[[ a comment on
     several lines ]]
local count = 0                   -- a local variable (use local almost always)
speed = 128                       -- a global variable, seen by every file
local name, open = "Mine", true   -- several at once
local nothing = nil               -- nil: no value; only nil and false are false

-- numbers: 12  3.5  1e3  0xFF     text: "a"  'b'  [[on several lines]]
local x = 7 // 2 + 7 % 2 + 2 ^ 3  -- 3 + 1 + 8: floor division, remainder, power
local line = "Stock: " .. count   -- .. joins text (and numbers)
local size = #line                -- # is the length of a text or a list
-- compare: == ~= (or !=) < > <= >=      logic: and or not

if count > 10 then
  print("many")
elseif count > 0 then
  print("some")
else
  print("none")
end

while count < 3 do count = count + 1 end
repeat count = count - 1 until count == 0
for i = 1, 10 do end                      -- 1, 2 ... 10
for i = 10, 1, -2 do end                  -- 10, 8 ... 2
for i, v in ipairs({"a", "b"}) do end     -- a list, in order
for k, v in pairs({x = 1, y = 2}) do end  -- every key of a table
for v in {"a", "b"} do end                -- the values of a list
-- break leaves the loop

local function area(w, h)
  return w * h                    -- a function returns one value
end
local function corner(w, h)
  return {x = w, y = h}           -- several values: return a table
end

local ores = {"iron", "gold"}             -- a list: ores[1] is "iron"
local stack = {name = "iron", count = 64} -- a record: stack.name, stack["count"]
ores[#ores + 1] = "copper"                -- add at the end
stack.count = nil                         -- remove a key

local loud = ("hello"):upper()   -- string functions work as methods
local r = pcall(area, 2, 3)      -- r.ok, then r.value or r.error

local timer = os.start_timer(1)
while true do
  local e = os.pull_event()
  if e.name == "timer" and e.id == timer then
    timer = os.start_timer(1)     -- every second: redraw, read the sensors...
  elseif e.name == "redstone" then
    print("left: " .. rs.get("left"))
  elseif e.name == "click" then
    print("click at " .. e.x .. ", " .. e.y)
  elseif e.name == "char" and e.char == "q" then
    break
  end
end

local function clamp(x, low, high)
  return math.max(low, math.min(high, x))
end
local rpm = clamp(math.floor(rs.get("back") * 256 / 15), 0, 256)

local vault = peripheral.find("inventory")
if vault == nil then error("no inventory found") end
print(vault.count("minecraft:iron_ingot") .. " iron ingots")

local function save(path, settings)
  local lines = {}
  for k, v in pairs(settings) do table.insert(lines, k .. "=" .. tostring(v)) end
  fs.write(path, table.concat(lines, "\n"))
end

local function load(path)
  local settings = {}
  local text = fs.read(path)
  if text == nil then return settings end
  for line in string.split(text, "\n") do
    local eq = string.find(line, "=")
    if eq then settings[string.sub(line, 1, eq - 1)] = string.sub(line, eq + 1) end
  end
  return settings
end

save("settings", {target = 128, mode = "auto"})
print(tonumber(load("settings").target) + 1)

129

-- the depot
net.broadcast({item = "minecraft:iron_ingot", count = 64}, "stock")

-- the control room
while true do
  local m = net.receive()
  if m.channel == "stock" then print(m.data.item .. ": " .. m.data.count) end
end

local r = pcall(fs.write, "log", "pressed: 12")
if not r.ok then print("could not save: " .. r.error) end