What Is Lua?

Lua is a small programming language. It is designed to be embedded inside another program, which means a host application can give Lua a carefully chosen set of functions and data.

OpenMW is the host. OpenMW starts Lua scripts, decides when they run, and provides engine modules such as openmw.core, openmw.world, and openmw.ui.

That distinction matters. Lua itself does not know what a cell, actor, record, or Morrowind save is. OpenMW teaches the script those things through its API.

The pieces you need first

Lua stores values in local variables:

local greeting = 'Hello from Lua.'
local visits = 3
local enabled = true

It groups related values in tables:

local player = {
    name = 'Nerevarine',
    visits = 3,
}

print(player.name)

Functions take values and may return values:

local function greetingFor(name)
    return 'Hello, ' .. name .. '.'
end

print(greetingFor('Nerevarine'))

Control flow chooses what happens:

if player.visits > 0 then
    print('Welcome back.')
else
    print('First visit.')
end

The .. operator joins strings. nil means “there is no value.” A missing table field usually produces nil, which is why this is common:

local cell = player.currentCell
if cell then
    print(cell.name)
end

Lua in one sentence

Lua is a language for describing data and behavior. OpenMW is the program that gives that behavior access to a game world.

Do not try to learn every corner of Lua before writing a script. Continue to Learn Enough Lua to Be Dangerous, then return to Lua's authoritative references when a syntax question appears.

Learn more

• Programming in Lua is the Lua project's recommended starting book. The freely available first edition describes Lua 5.0, so use it for language concepts and check the version notes below.
• The Lua 5.1 Reference Manual is the relevant language reference for OpenMW's Lua baseline.
• OpenMW Lua Mental Model explains what OpenMW adds around the language.