Lua basic grammar learning

Learning links

1. https://blog.csdn.net/jiangwei0512/article/details/51057649
2. https://blog.csdn.net/THIOUSTHIOUS/article/details/86552762
3. https://segmentfault.com/a/1190000018641801
4. https://cloud.tencent.com/developer/article/1043931
5. https://github.com/openresty/lua-nginx-module
6. https://blog.51cto.com/xikder/2331649 Nginx Lua Implementation phase of

1、 notes

Lua The notes used are as follows ：

--  Single line comments use 
--[[
     Multiline comments use 
     Multiline comments use 
]]


--[[
if x > 1 then
    --  notes 1
else
    --  notes 2
end
--]]

2、 data type

Lua Of 8 Basic types ：

Some notes ：

• nil Type only nil Such a value
• boolean There are two values true and false. in addition Lua All values in can be used in conditional statements , Besides false and nil Said the false , Everything else means true . such as 0, It means true .
• The value type is only number, No, int、float Other types .
• string You can use double quotes , You can also specify with single quotation marks . You can also use [[ It's a string ]],[[]] It can contain multiple lines , Can be nested , And do not explain the transfer character .
• function Like other types mentioned above , It belongs to the first kind of value , That is to say, it can also exist in ordinary variables .
• table、userdata and thread I'll talk about it later .

3、table library

do
    --> table.concat   Connect   function 

    tab = {
    "a", "c", "d", "b"}

    --(1)
    --  One parameter , Parameter is   surface (tab), The function is to connect  tab  All of the  value
    print(table.concat(tab))   
    -->  Output results ： acdb

    --(2)
    --  Two parameters , Parameter one ： surface (tab), Parameter two ： Separator (nil),
    --  The function is to connect tab All of the value,value  In between  nil  separate 
    print(table.concat(tab, nil))  
    -->  Output results ： acdb

    --(3)
    --  Three parameters , Parameter one ： surface (tab), Parameter two ： Separator  (" @@ "),
    --  Parameter 3 ： The starting position (2), The function is to connect tab All of the value, The location is from 1 The beginning of the calculation 
    -- value  In between  " @@ "  separate ,  from  tab  The second value Start connecting ,
    --  To  tab  Of  end 
    print(table.concat(tab, " @@ ", 2))  
    -->  Output results ： c @@ d @@ b

    --(4)
    --  Four parameters , Parameter one ： surface (tab), Parameter two ： Separator  (" - "),
    --  Parameter 3 ： The starting position (2), Parameter 4 ： End connection location , The function is to connect 
    --  Pick up tab All of the value,value  In between  " - "  separate ,  from  tab 
    --  The second value   Start connecting , To  tab  Of   The first  3  individual  value End connection 

    print( table.concat(tab, " - ", 2, 3))  
    -->  Output results ： c - d
    print(table.concat(tab, " ## \n", 2, 4))   
    -->  Output results ：
    --> c ##
    --> d ##
    --> b

    --(5)
    for i,v in ipairs(tab) do
        print(i,v)
    end
    -->  Output results ：
    -- 1      a
    -- 2      c
    -- 3      d
    -- 4      b

    --  explain  table.concat  Will not change   original  table  namely (tab)  Structure 
end

4、 expression

1. ~= amount to c In language !=, It's not equal to .
2. table、userdata and function It's quoting comparison , Only two variables pointing to the same object are equal .
3. The logical operator is "and or not", But here and and or The meaning follows c Languages are different ：
   a and b： If a by false, Then return to a, Otherwise return to b;
   a or b ： If a by true, Then return to a, Otherwise return to b.
4. “…” Two points , Represents a character connector ; If the operand is number, Is converted to a string ：

print(1 … 2) --> 12, Be careful … You need a space before and after , Otherwise, an error will be reported
Note that there 1 … There is a space between , Otherwise, it will report a mistake .
But if it's a string, you don't need ：

print("hello".."world")	--> helloworld

5、 The structure of the watch

Here is a basic example ：

table1 = {
    }                             -->  Empty table 
names = {
    "jack", "john", "jimmy"}       -->  List initialization 
print(names[1])                         --> jack, Subscript from 1 Start 
names[4] = "jason"                      -->  Dynamic addition 
print(names[4])                         --> jason
print(names[5])                         --> nil, Because it doesn't exist 
a = {
    x = 0, y = 1}                      --> record Form initialization 
print(a.x)                              --> 0
print(a["x"])                           --> 0, Another way to express 
b = {
    "helloworld", x = 1, "goodbye"}    --> Mixed form 
print(b[1])                             --> helloworld
print(b.x)                              --> 1
print(b[2])                             --> goodbye
-- print(b.1)                           -->  There's no such thing 

Commas can be used to separate tables , You can also use semicolons .
There is a more general form ：

a = {
    ["+"] = "add", ["-"] = "sub", ["*"] = "mul", ["/"] = "div", }  -->  There can be a comma after 
print(a["+"])   --> add
b = {
    [1] = "one", [2] = "two", [3] = "three"}
print(b[1])     --> one

6、 Control statement

IF sentence

if xxx then xxx end
if xxx then xxx else xxx end
if xxx then xxx elseif xxx then xxx else xxx end

elseif There can be many , Be careful else and if There is no space in the middle ！！

WHILE sentence

while xxx do xxx end

REPEAT-UNTIL sentence

repeat xxx until xxx

FOR sentence

for var=exp1,exp2,exp3 do xxx end

here for The sentence inside means var With exp3 by step, from exp1 To exp2.

There are a few points to pay attention to ：

• How many? exp It will only run once , And in for Before the cycle ;
• var It's a local variable ;
• Don't change during the cycle var.

for x,y,z in xxx do xxx end

BREAK and RETURN sentence
break Exit the current loop ;return Exit the function and return the result .
Be careful break and return Can only be used in one block Ending . If you really want to use it in another place sometimes , In this way ：

do break/return end

7、 function

Definition of function ：

function funcName (args)
    states
end

About function calls , If there are no parameters , Need to use ();

If the parameter is a string or table construction , Don't have to ().

Lua The matching of real parameters and formal parameters in functions is also less particular , Actual parameters are more than formal parameters , The redundant part will be ignored ; Fewer arguments than formal ones , Less formal parameters will be nil. This is consistent with the multivariable assignment .

Function can return multiple values ：

function func (void)
    return 1,2
end
 
a,b = func()
print(a)    --> 1
print(b)    --> 2

adopt () You can force a function to return a value ：

function func (void)
    return 1,2
end
 
print(func())       --> 1 2
print((func()))     --> 1

Lua There can be variable parameters . Use … Three dots indicate , Use a function called arg Of table Said parameters ,arg There is also a domain in n Indicates the number of parameters .
Here is an example ：

function func_1(...)
    print("The number of args: " .. #{...})
    for i,v in ipairs({
    ...}) do
        print(i,v)
    end
end
func_1(0, 1, 2, 3)

The result of printing is ：

The number of args: 4
1       0
2       1
3       2
4       3

Lua And Nginx

When Nginx When the standard module and configuration cannot flexibly adapt to the system requirements , You can consider using it Lua Expand and customize Nginx service .OpenResty It integrates a large number of sophisticated Lua library 、 Third-party module , It can be easily built to handle ultra-high concurrency 、 Highly scalable Web service , So here we choose OpenResty Provided lua-nginx-module programme .

lua-nginx-module The module is already Lua Provides a wealth of Nginx call API, Every API Each has its own environment , See for a detailed description Nginx API for Lua. Here are only the basic API Use .

First, one Lua Script Services , The configuration file is as follows ：

location ~ /lua_api {
      
    #  Exemplary Nginx Variable  
    set $name $host;
    default_type "text/html";  
    #  adopt Lua File content processing 
    content_by_lua_file /home/www/nginx-api.lua;  
}

content_by_lua_file ： In the specified file <path-to-lua-script-file> contain  Lua  Code 

Nginx Processing sequence stage

（1）post-read
 Read request content stage ,nginx After reading and parsing the request header, it starts running immediately ;

（2）server-rewrite
server Request address rewrite phase ;

（3）find-config
 Configuration search phase , Used to complete the current request and location Pairing between counterweights ;

（4）rewrite
location Request address rewrite phase , When ngx_rewrite Instructions for location in , It is at this stage that it runs ;

（5）post-rewrite
 Request address rewrite submission phase , When nginx complete rewrite Internal jump action required by stage , If rewrite If there is such a requirement in the stage ;

（6）preaccess
 Access rights check preparation stage ,ngx_limit_req and ngx_limit_zone Run at this stage ,ngx_limit_req You can control the access frequency of requests ,ngx_limit_zone You can control the concurrency of access ;

（7）access
 Permission check stage ,ngx_access Run at this stage , Configuration instructions mostly perform tasks related to access control , Such as checking the access rights of users , Check the source of the user IP Is it legal ;

（8）post-access
 Access check submission phase ;

（9）try-files
 Configuration item try_files Processing stage ;

（10）content
 Content generation stage , It is the most important stage of all request processing stages , Because the instructions at this stage are usually used to generate HTTP Respond to the content of ;

（11）log

Log module processing stage ;

ngx_lua Operation instruction

ngx_lua Belong to nginx Part of , Its execution instructions are contained in nginx Of 11 Step by step , The corresponding processing stage can do plug-in processing , Pluggable architecture , however ngx_lua Not all phases will run ; In addition, the instructions can be in http、server、server if、location、location if Configure several ranges ：