Article Directory

One: shell function
Two: shell array

One: shell function

The essence of the Shell function is a piece of script code that can be reused. This code is written in advance, placed in a designated location, and can be called directly when used.
The functions in Shell are similar to functions in other programming languages such as C++, Java, Python, C#, but differ in the details of the syntax.
The syntax format of Shell function definition is as follows:

function name() {
    
          #function是shell中的关键字，专门用来定义函数  name是函数名
  statements           #statements是函数要执行的代码，也就是一组语句；
  [return value]       #return value表示函数的返回值，其中return是shell关键字，专门用在函数中返回一个值；这一部分可以写也可以不写。
}                      #由{ }包围的部分称为函数体，调用一个函数，实际上就是执行函数体中的代码。

1.1: Simplified writing of function definition

If you find it troublesome, you can omit the function keyword when defining the function:

name() {
    
    
  statements
  [return value]
}

If you write the function keyword, you can also omit the parentheses after the function name:

function name {
    
    
  statements
  [return value]
}

I recommend using standard writing so that no matter who writes this script, you can understand it.

[root@localhost opt]#vim jia.sh
#!/bin/bash
sum () {
    
    
s=`expr 5 + 3`
echo $s
}
sum
[root@server1 ~]# sh a.sh 
8

sum () {
    
    
s=`expr $1 + $2`
echo $s
}
sum 5 6
[root@server1 ~]# sh a.sh 
11

在这里插入代码片

sum () {
    
    
 return $(($1 + $2))
}
sum 3 4
echo $?
[root@server1 ~]# sh a.sh 
7

function sum(){
    
    
  #命令序列
  read -p "请输入第一个整数： " num1
  read -p "请输入第一个整数： " num2
  SUM=$[$num1+$num2]
  echo "和：$SUM"
}
sum
[root@server1 ~]# sh a.sh 
请输入第一个整数： 5
请输入第一个整数： 4
和：9

function sum(){
    
    
  #命令序列
  read -p "请输入第一个整数： " num1
  read -p "请输入第一个整数： " num2
  SUM=$[$num1+$num2]
  echo $SUM
}
tom=`sum 4 2`
let tom+=1
echo $tom
[root@server1 ~]# sh a.sh 
请输入第一个整数： 6
请输入第一个整数： 3
10

1.2: The scope of the function

Functions in Shell scripts are only valid in the current Shell environment
Variables in ShelI script are globally effective by default
Use the local command to limit the variable to the function

Example

The internal variables of the function are implemented by local
By defining the myfun function, set the local variable i inside it
Assign values inside and outside the function to verify the results

function sh(){
    
    
  #命令序列
  read -p "请输入第一个整数： " num1
  read -p "请输入第一个整数： " num2
  s=$[$num1+$num2]
  jerry=20
  echo 函数内$jerry
  echo 和:$s
}
sh
  echo 函数外$jerry
[root@server1 ~]# sh a.sh 
请输入第一个整数： 2
请输入第一个整数： 3
函数内20
和:5
函数外20

local defines global variables

function sh(){
    
    
  #命令序列
  read -p "请输入第一个整数： " num1
  read -p "请输入第一个整数： " num2
  s=$[$num1+$num2]
  local jerry=20     #local定义全局变量
  echo 函数内$jerry
  echo 和:$s
}
sh
  echo 函数外$jerry
[root@server1 ~]# sh a.sh 
请输入第一个整数： 2
请输入第一个整数： 4
函数内20
和:6
函数外

1.3: Recursive function

Call your own function
Example
Recursively traverse the directory
Realize by defining the recursive function list_files

#!/bin/bash
function list_files(){
    
    
 for s in `ls $1`
 do
 if [ -d "$1/$s" ]
  then
     echo "$2$s"
     list_files "$1/$s" "$2"
   else
     echo "$2$s"
   fi
   done
}
list_files "/var/log"
#$1表示/var/log
#$s表示/var/log下一个目录
#$2表示指定格式 子目录一定要做一个首行缩进
[root@server1 ~]# sh bianli.sh 
amanda
anaconda
anaconda.log
ifcfg.log
journal.log
ks-script-j10KNj.log
ks-script-mW8ioG.log
packaging.log
program.log
……

Two: shell array

2.1: Application scenarios include

Application scenario package length
Get array length
Get element length
Iterate over elements
Element slice
Element replacement
Element deletion
…

2.2: Description of the array

Array: Put the same type of data collection. There are many
application scenarios: the grades and names of
classmates [11,22,33,44] Open up a continuous space in the memory
Use the
array name arr arr=(44) ,33,22,11)
Array elements: 44 33 22 11 are all
Length of the array: arr has 4 elements
Array subscript: 33 elements are below 1 (for example, 11 subscript is 3 22 subscript is 2)
for temporary Scalar in array
do
done

2.3: Array definition method

method one

数组名=（shuai0 shuai1 shuai2...）

Method Two

数组名=（[0]=shuai [1]=shuai [3]=shuai...）
[root@server1 test]# num=([0]=44 [1]=33 [2]=22 [3]=11)
[root@server1 test]# echo ${num[*]}
44 33 22 11

Method Three

列表名="shuai0 shuai1 shuai2.."
数组名= （$列表名）
[root@server1 test]# tom=" 1 2 3 4 "
[root@server1 test]# num=($tom)
[root@server1 test]# echo ${num[*]}
1 2 3 4

#!/bin/bash
list=`cat test.txt`
echo $list
[root@server1 test]# sh test.sh
5 6 7 8
#!/bin/bash
list=`cat test.txt`
f=($list)
echo ${
    
    f[*]}
[root@server1 test]# sh test.sh
5 6 7 8

Method three is
often done is to replace an element

数组名[0]="shuai"
数组名[1]="shuai"
数组名[2]="shuai"

[root@server1 test]# num=([0]=2 [1]=5 [2]=6 [3]=8)
[root@server1 test]# echo ${num[*]}
2 5 6 8
[root@server1 test]# num[2]=10
[root@server1 test]# echo ${num[*]}
2 5 10 8

2.3.1: to 100 array

#!/bin/bash
for ((i=0;i<99;i++))
 do
 tom[$i]=$[$i+1]
 done
echo ${
    
    tom[*]} 
[root@server1 test]# sh 1_100.sh 
1 2 3 4 5 6 7 8 9 ……

2.3.2: Create odd arrays from 1 to 100

#!/bin/bash
for ((i=0;i<99;i+=2))
 do
 tom[$i]=$[$i+1]
 done
echo ${tom[*]}          
[root@server1 test]# sh 1_100.sh 
1 3 5 7 9 11 13 15 ……