A quick overview of basic Lua language concepts is shown below.
Review chapters 1-5 of the Lua programming guide for more details.
Comments
--A comment
--[[ A
comment block
]]
Variables
local var1 -- Declaring a variable
local var2; -- Semicolon to end a statement (chunk) is optional
local var3 = nil -- nil is the default value for all uninitialized variables - similar to null in other languages
local VaR4 = "AbC" -- variables and strings are case-sensitive
local var5 = {} -- Declaring an array (a.k.a table)
Reserved names
and break do else elseif
end false for function if
in local nil not or
repeat return then true until
while
Variable types
local string = "Hello world"
local number = 10
local number2 = 10.4
local boolean = true
local function = type()
Escaping characters in strings
local string = "one line\nnext line\n\"in quotes\", 'in quotes'"
Tables - similar to arrays in other languages
local a = {} -- create a table
local a = {1,2,3} -- accessed as a[1]=1, a[2]=2, a[3]=3
local a = {one=1,two=2,three=3} -- accessed as a["one"]=1, a["two"]=2, a["three"]=3 or a.one=1, a.two=2, a.three=3
-- items are placed starting at [1] position when declaring like this
local a = {"one","two","three"} -- accessed as a[1]="one", a[2]="two", a[3]="three"
-- replacing array items
a[1] = "four"
a["x"] = "string"
a["y"] = 5
Operator precedence
^ (exponential)
not - (unary operator)
* /
+ -
.. (concatenation)
< > <= >= ~= == (relational operators)
and (boolean operator)
or (boolean operator)
Parentheses control precedence
(a+i) < ((b/2)+1)
Concatenation
local b = "Hello ".."World"
local b = 0 .. 1 -- spacing required for numbers
Multiple assignments
a,b = 1,2
a,b = f() -- functions can return multiple results
If/then/else
if a<0 then a = 0 end
if a<b then return a else return b end
While loop
local i = 1
while a[i] do
print(a[i])
i = i + 1
end
For loop
for i=1,f(x) do dw.log.exception("INFO",i) end
for i=10,1,-1 do dw.log.exception("INFO",i) end
-- log all values of array 'a'
for i,v in ipairs(a) do dw.log.exception("INFO",v) end