Learn Lua grammar in 10 minutes – follow the official examples

Lua is a simple and lightweight scripting language, examples from Lua official small examples, all learn to use

— Example 1 — Helloworld

Print it

-- Classic hello program.

print("helloworld")



-------- Output ------

hello
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Example 2

There are two kinds of comments, two horizontal lines, and two square brackets for multi-line comments

-- Single line comments in Lua start with double hyphen.

--[[ Multiple line comments start with double hyphen and two square brackets. and end with two square brackets. ]]

-- And of course this example produces no
-- output, since it's all comments!

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Example 3 — variables.

Variables are not declared, they are used directly, and there is no type HHH is similar to py

-- Variables hold values which have types, variables don't have types.

a=1
b="abc"
c={}
d=print

print(type(a))
print(type(b))
print(type(c))
print(type(d))


-------- Output ------

number
string
table
function

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— Example 4 — variable name.

Note: Same as C

-- Variable names consist of letters, digits and underscores.
-- They cannot start with a digit.

one_two_3 = 123 -- is valid varable name

-- 1_two_3 is not a valid variable name.

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Variable names can be alphanumeric and underscore but must not start with a number

— Reserved words.

It starts with underscore

-- The underscore is typically used to start special values
-- like _VERSION in Lua.

print(_VERSION)

-- So don't use variables that start with _,
-- but a single underscore _ is often used as a
-- dummy variable.


-------- Output ------

Lua 5.1
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An underscore is the beginning of reserved words. Variables cannot begin with _

Example 6 — Case sensitive.

Don’t have to explain

-- Lua is case sensitive so all variable names & keywords
-- must be in correct case.

ab=1
Ab=2
AB=3
print(ab,Ab,AB)



-------- Output ------

1       2       3
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Case sensitive

— Example 7 — reserved keywords.

Capitalized is not a keyword

-- Lua reserved words are: and, break, do, else, elseif,
-- end, false, for, function, if, in, local, nil, not, or,
-- repeat, return, then, true, until, while.

-- Keywords cannot be used for variable names,
-- 'and' is a keyword, but AND is not, so it is a legal variable name.
AND=3
print(AND)



-------- Output ------

3
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— Example 8 — string

3, single quotes, double quotes, and multiple lines (multiple lines with newlines)

a="single 'quoted' string and double \"quoted\" string inside"
b='single \'quoted\' string and double "quoted" string inside'
c= [[ multiple line
with 'single'
and "double" quoted strings inside.]]

print(a)
print(b)
print(c)


-------- Output ------

single 'quoted' string and double "quoted" string inside
single 'quoted' string and double "quoted" string inside
 multiple line
with 'single'
and "double" quoted strings inside.
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Three ways to represent a string

— Example 9 — strange assignment methods are supported

-- a,b = b,a is valid
a,b,c,d,e = 1.2.3.'four'.'five'
print(a,b,c,d,e)

-------- Output ------
1       2       3       four    five
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— Example 10 — a strange way to assign values is to swap variables

-- Multiple assignments allows one line to swap two variables.

print(a,b)
a,b=b,a
print(a,b)

-------- Output ------

1       2
2       1
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— The number of people in the world

You can connect strings and numbers with two dots

-- Multiple assignment showing different number formats.
-- Two dots (..) are used to concatenate strings (or a
-- string and a number).

a,b,c,d,e = 1.1.123.1E9.- 123..0008.
print("a="..a, "b="..b, "c="..c, "d="..d, "e="..e)



-------- Output ------

a=1     b=1.123 c=1000000000    d=- 123.  e=0.0008
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— Example 12 — print without parentheses?

-- More writing output.

print "Hello from Lua!"
print("Hello from Lua!")



-------- Output ------

Hello from Lua!
Hello from Lua!
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— Example 13 — can use stdout

-- io.write writes to stdout but without new line.

io.write("Hello from Lua!")
io.write("Hello from Lua!")

-- Use an empty print to write a single new line.
print(a)-------- Output ------Hello from Lua! Hello from Lua!Copy the code

Print can print a new line

— Example 14 — array.

Array, officially written Tables, can be accessed using subscripts

-- Simple table creation.

a={} -- {} creates an empty table
b={1.2.3} -- creates a table containing numbers 1,2,3
c={"a"."b"."c"} -- creates a table containing strings a,b,c
print(a,b,c) -- tables don't print directly, we'll get back to this!!


-------- Output ------

table: 008A48A8 table: 008A4420 table: 008A4768


The default initial index of a table in Lua usually starts with 1.
> b = {4.5.6.7.8}
> print(b)
table: 009B9978
> print(b[0])
nil
> print(b[1])
4
> print(b[2])
5
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— Example 15 subscripts can be strings

-- Associate index style.

address={} -- empty address
address.Street="Wyman Street"
address.StreetNumber=360
address.AptNumber="2a"
address.City="Watertown"
address.State="Vermont"
address.Country="USA"

print(address.StreetNumber, address["AptNumber"])



-------- Output ------

360     2a
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— Example 16 — if statement.

Remember then and end

-- Simple if.

a=1
if a==1 then
    print ("a is one")
end


-------- Output ------

a is one
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— Example 17 — if else statement.

if else end

b="happy"
if b=="sad" then
    print("b is sad")
else
    print("b is not sad")
end


-------- Output ------

b is not sad
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if then else end

— Example 18 — if elseif else statement

Many branches

c=3
if c==1 then
    print("c is 1")
elseif c==2 then
    print("c is 2")
else
    print("c isn't 1 or 2, c is ".tostring(c))
end


-------- Output ------

c isn't 1 or 2, c is 3
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if then elseif then else end

— Example 19 — Conditional assignment?

It’s kind of like the triadic operator for C

Is b = (a == 1)? “one”: “not one”;

-- value = test and x or y

a=1
b=(a==1) and "one" or "not one"
print(b)

-- is equivalent to
a=1
if a==1 then
    b = "one"
else
    b = "not one"
end
print(b)


-------- Output ------

one
one
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— Example 20 — while

While do end (~= = C! =)

a=1
while a~=5 do -- Lua uses ~= to mean not equal
    a=a+1
    io.write(a.."")
end


-------- Output ------

2 3 4 5
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— Example 21 — repeat until statement.

do while?

a=0
repeat
    a=a+1
    print(a)
until a==5


-------- Output ------

1
2
3
4
5
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— Example 22 — for loop

For [1, 4] do end

-- Numeric iteration form.

-- Count from 1 to 4 by 1.
for a=1.4 do io.write(a) end

print(a)-- Count from 1 to 6 by 3.
for a=1.6.3 do io.write(a) end


-------- Output ------

1234
14
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for do end

— Example 23 — Foreach? .

For can also use *(foreach?)

-- Sequential iteration form.

for key,value in pairs({1.2.3.4}) do print(key, value) end


-------- Output ------

1       1
2       2
3       3
4       4
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Example 24 — Prints an array with pairs.

pairs?

-- Simple way to print tables. ## iterator

a={1.2.3.4."five"."elephant"."mouse"}

for i,v in pairs(a) do print(i,v) end


-------- Output ------

1       1
2       2
3       3
4       4
5       five
6       elephant
7       mouse
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— Example 25 — break out of the loop

-- break is used to exit a loop.
a=0
while true do
    a=a+1
    if a==10 then
        break
    end
end

print(a)


-------- Output ------

10

Press 'Enter' key for next example

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— Example 26 — function

-- Define a function without parameters or return value.
function myFirstLuaFunction(a)
    print("My first lua function was called")
end

-- Call myFirstLuaFunction.
myFirstLuaFunction()


-------- Output ------

My first lua function was called

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Example 27 — a function that returns a value

-- Define a function with a return value.
function mySecondLuaFunction(a)
    return "string from my second function"
end

-- Call function returning a value.
a=mySecondLuaFunction("string")
print(a)

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— Example 28 — returns a bunch of values

-- Define function with multiple parameters and multiple return values.
function myFirstLuaFunctionWithMultipleReturnValues(a,b,c)
    return a,b,c,"My first lua function with multiple return values".1.true
end

a,b,c,d,e,f = myFirstLuaFunctionWithMultipleReturnValues(1.2."three")
print(a,b,c,d,e,f)


-------- Output ------

1       2       three   My first lua function with multiple return values 1true
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— Example 29 — local

Default variables are global variables, and local variables are declared with local

-- All variables are global in scope by default.

b="global"

-- To make local variables you must put the keyword 'local' in front.
function myfunc(a)
    local b=" local variable"
    a="global variable"
    print(a,b)
end

myfunc()
print(a,b)


-------- Output ------

global variable  local variable
global variable global

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All variables are global in scope by default.

— Example 30 — Format printf

-- An implementation of printf.

function printf(fmt, ...)
    io.write(string.format(fmt, ...) )end

printf("Hello %s from %s on %s\n".os.getenv"USER" or "there"._VERSION.os.date())


-------- Output ------

Hello there from Lua 5.1 on 08/05/19 09:34:49
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Example 31 standard library?

--[[ Standard Libraries Lua has standard built-in libraries for common operations in math, string, table, input/output & operating system facilities. External Libraries Numerous other libraries have been created: sockets, XML, profiling, logging, unittests, GUI toolkits, web frameworks, and many more. ]]



-------- Output ------
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— Example 32 — Math library.

-- Math functions:
-- math.abs, math.acos, math.asin, math.atan, math.atan2,
-- math.ceil, math.cos, math.cosh, math.deg, math.exp, math.floor,
-- math.fmod, math.frexp, math.huge, math.ldexp, math.log, math.log10,
-- math.max, math.min, math.modf, math.pi, math.pow, math.rad,
-- math.random, math.randomseed, math.sin, math.sinh, math.sqrt,
-- math.tan, math.tanh

print(math.sqrt(9), math.pi)


-------- Output ------

3       3.1415926535898
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— Example 33 — String library.

-- String functions:
-- string.byte, string.char, string.dump, string.find, string.format,
-- string.gfind, string.gsub, string.len, string.lower, string.match,
-- string.rep, string.reverse, string.sub, string.upper

print(string.upper("lower"),string.rep("a".5),string.find("abcde"."cd"))


-------- Output ------

LOWER   aaaaa   3       4
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— Example 34 — Table library.

-- Table functions:
-- table.concat, table.insert, table.maxn, table.remove, table.sort

a={2}
table.insert(a,3);
table.insert(a,4);
table.sort(a,function(v1,v2) return v1 > v2 end)
for i,v in ipairs(a) do print(i,v) end


-------- Output ------

1       4
2       3
3       2
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— Example 35 — Input /output library.

-- IO functions:
-- io.close , io.flush, io.input, io.lines, io.open, io.output, io.popen,
-- io.read, io.stderr, io.stdin, io.stdout, io.tmpfile, io.type, io.write,
-- file:close, file:flush, file:lines ,file:read,
-- file:seek, file:setvbuf, file:write

       print(io.open("file doesn't exist"."r"))


-------- Output ------

nil     file doesn't exist: No such file or directory 2Copy the code

— Example 36 — OS library

-- OS functions:
-- os.clock, os.date, os.difftime, os.execute, os.exit, os.getenv,
-- os.remove, os.rename, os.setlocale, os.time, os.tmpname

print(os.date())


-------- Output ------

08/05/19 09:36:36
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— Example 37 — External libraries

External libraries need to be imported using require

-- Lua has support for external modules using the 'require' function
-- INFO: A dialog will popup but it could get hidden behind the console.

require( "iuplua" )
ml = iup.multiline
    {
    expand="YES",
    value="Quit this multiline edit app to continue Tutorial!",
    border="YES"
    }
dlg = iup.dialog{ml; title="IupMultiline", size="QUARTERxQUARTER",}
dlg:show()
print("Exit GUI app to continue!")
iup.MainLoop()


-------- Output ------

failed to load & run sample code
error loading module 'iuplua' from file 'C:\Dev\Lua\clibs\iuplua51.dll':
        The specified module could not be found.
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There are many examples of this

--[[ To learn more about Lua scripting see Lua Tutorials: http://lua-users.org/wiki/TutorialDirectory "Programming in Lua" Book: http://www.inf.puc-rio.br/~roberto/pil2/ Lua 5.1 Reference Manual: Start/designed / / Documentation/Lua Lua 5.1 Reference Manual Examples: Start/Examples/designed/Lua]]

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