Programming in Lua (5.0) Tutorial — Reference Manual — Short Reference — IBM intro: Embeddable scripting with Lua — Linux Journal intro: A Look at Lua

Use www.slackbuilds.org

External addons / Packages for Lua:

• Automated "Rocks"
• Manual

#!/usr/bin/lua

Use global table arg

local inp= io.stdin:read() -- Read a line from stdion
print()                    -- Print a line to stdout
io.stdout:write()          -- Print a string to stdout
io.stderr:write()          -- Print a string to stderr

for i = 0,24,4 do -- start, end (including), step
    print(i)
end

Use # operator

-- Iterate over array part:
for i,v in ipairs(now) do print(i,v) end
 
-- Iterate over complete table:
for k,v in pairs(now) do print(k,v) end

#!/usr/bin/lua
 
-- Numbers:
a=3 -- a contains 3
b=a -- b contains 3
a=4 -- a contains 4, b still contains 3
print(a,b) -- 4  3
 
-- Booleans:
a=true; b=a; a=false
print(a,b) -- false  true
 
-- Strings:
a="World"  -- a points to the string "World"
b=a        -- b points to the same string
a="Hello"  -- a points to "World", b still points to "Hello"
print(a,b) --> Hello  World
 
-- Functions:
a= function() print("World") end
b=a
-- a and b point to the same function:
print(a,b) --> function: 0x80500e8  function: 0x80500e8
a= function() print("Hello") end
-- a points to a new function and b still points to the old function:
print(a,b) --> function: 0x8050a48  function: 0x80500e8
a() -- Hello
b() -- World

#!/usr/bin/lua
 
-- Tables:
a={3}
b=a;
-- a and b point to the same table:
print(a,b) -- table: 0x80509e0	table: 0x80509e0
print(a[1],b[1]) -- 3  3
a[1]=4;
print(a[1],b[1]) -- 4  4
b[1]=5
print(a[1],b[1]) -- 5  5
 
a={6}
-- a points to a new table and b still points to the old table:
print(a,b) -- table: 0x8050a30	table: 0x80509e0
print(a[1],b[1]) -- 6  5
b[1]=7
print(a[1],b[1]) -- 6  7

needs rework!

This is simliar to Go

A throw/catch mechanism is possible with error() / pcall(). More

-- rectangle prototype:
rectangle_proto= {species="rectangle"}
function rectangle_proto:area() return self.width * self.height end
 
-- rectangle constructor:
function new_rectangle(width, height)
    local rectangle= {width= width, height= height}
    setmetatable(rectangle, {__index=rectangle_proto})
    return rectangle
end
 
-- rectangle usage:
rectangle= new_rectangle(3,4)
print(rectangle:area())  --> 12
print(rectangle.species) --> rectangle
 
 
-- circle prototype:
circle_proto= {species="circle"}
function circle_proto:area() return self.radius^2 * math.pi end
 
-- circle constructor:
function new_circle(radius)
    local circle= {radius= radius}
    setmetatable(circle, {__index=circle_proto})
    return circle
end
 
circle= new_circle(1)
print(circle:area())  --> 3.14
print(circle.species) --> circle

Classic single inheritance chain:

-- Inheritance: shape prototype:
shape_proto= {family="shape"}
function shape_proto:get_species() return self.species end
function shape_proto:get_family() return self.family end
 
setmetatable(rectangle_proto, {__index=shape_proto})
setmetatable(circle_proto, {__index=shape_proto})
 
print(circle:get_family().."/"..circle:get_species()) --> shape/circle
print(rectangle:get_family().."/"..rectangle:get_species()) --> shape/rectangle

• http://code.google.com/p/go-wiki/wiki/GoForCPPProgrammers#Interfaces
• Option 1: No metatables. Just implant all methods of the interface directly into the table which represents the object. Simple
• Option 2: One metatable for every type. No metatable chain. Each type hast a dedicated factory and metatable. All implemented interface methods are copied into the metatable of the type. Saves space.

Lua print() does not look for a tostring() method directly in the table, instead it looks for a method called __tostring() in its metatable. Thus, to enable both print(myobject:tostring()) (explicit call) and print(myobject) (implicit call), provide the tostring() method in the prototype table of the object and set __tostring attribute of the metatable to that method:

-- rectangle prototype:
rectangle_proto= {}
function rectangle_proto:tostring() return "["..self.width.."|"..self.height.."]" end
 
-- rectangle constructor:
function new_rectangle(width, height)
    rectangle= {width= width, height= height}
    setmetatable(rectangle, {
        __index=rectangle_proto,
        __tostring=rectangle_proto.tostring
    })
    return rectangle
end
 
-- rectangle usage:
rectangle= new_rectangle(3,4)
print(rectangle:tostring()) --> [3|4]
print(rectangle)            --> [3|4]

This works also if tostring() is defined in the base clase:

-- shape as base class:
shape_proto= {}
function shape_proto:tostring() return "["..self.width.."|"..self.height.."]" end
 
-- rectangle prototype inherits from shape:
rectangle_proto= {}
setmetatable(rectangle_proto, {
    __index=shape_proto
})
 
-- rectangle constructor:
function new_rectangle(width, height)
    rectangle= {width= width, height= height}
    setmetatable(rectangle, {
        __index=rectangle_proto,
        __tostring=rectangle_proto.tostring
    })
    return rectangle
end
 
-- rectangle usage:
rectangle= new_rectangle(3,4)
print(rectangle:tostring()) --> [3|4]
print(rectangle)            --> [3|4]

To run some code sitting in a different file, use dofile()

To load global variables of an external (config) file into a table locally, you have to pass the table as environment:

config.lua

a="Harry"
b="Hirsch"

main.lua

#!/usr/bin/lua
 
local extenv={}
local chunk= loadfile("config.lua", "t" , extenv)
chunk()
 
for key,value in pairs(extenv) do
    io.write("[", key, "] = ", value, "\n")
end

result

[a] = Harry
[b] = Hirsch

See ModuleDefinition and LuaStyleGuide → Modules

module() is deprecated!

now= os.time()

-- Return a table containing hour, min, wday, day, ... of current time:
now = os.date("*t")
 
-- Return a table containing hour, min, wday, day, ... of a certain time:
atime = os.date("*t", timestamp)
 
-- Return a formated string of current time:
now = os.date("Today is %A") -- Today is Thursday

Source

Example:

-- global.lua
a=0
b=0
for i=1, 10000000 do
    a= b+1
    b= a
end

$time global.lua
real	0m1.178s
user	0m1.176s
sys	0m0.001s

-- local.lua
local a=0
local b=0
for i=1, 10000000 do
    a= b+1
    b= a
end

$time local.lua
real	0m0.161s
user	0m0.157s
sys	0m0.003s

#!/usr/bin/lua
 
co= coroutine.create(function()
    while true do
        io.stderr:write('co: waking up\n')
        local inp= io.stdin:read()
        io.stderr:write('co: read "'..inp..'", going to sleep\n')
        coroutine.yield(inp)
    end
end)
 
while true do
    io.stderr:write('main: going to sleep\n')
    local state, oup= coroutine.resume(co)
    io.stderr:write('main: waking up\n')
    print('> '..oup)
end