The use of if,case,for in shell scripts

Directory
I. Condition selection: If statement
Two. Conditional judgment: Case statement
Three. For loop

I. Condition selection: If statement

2. Single Branch
   if judgment condition; then
   Branch code with true condition
   Fi
   Example: Judging whether a number equals 10
   #!/bin/bash
   Read-p ' Enter a number ' num
   If [$num-eq];then
   echo This number equals 10
   Fi
4. Dual Branch
   if judgment condition; Then condition is true for the branch code
   Else condition is a false branch code
   Fi
   Example: Judging if a number is greater than 10
   #！ /bin/bash
   Read-p ' Enter a number ' num
   If [$num-gt];then
   echo this number is greater than 10
   Else
   echo this number is not greater than 10
   Fi

5. Multiple branches
   if judgment condition 1; Then condition is true for the branch code
   Elif judgment Condition 2; Then condition is true for the branch code
   Elif judgment Condition 3; Then condition is true for the branch code
   Else the above conditions are false branch codes
   Fi
   Example: Judging the range of a number

           #!/bin/bash        read -p ‘输入一个数字‘ num        if [ $num -lt 10 ];then             echo 该数字小于10        elif [ $num -ge 10 -a $num -lt 20  ];then              echo 该数字大于等于10小于20         elif [ $num -ge 20 -a $num -lt 50 ];then              cho 该数字大于等于20小于50         else                   echo 该数字大于等于50        fi      

   Two. Conditional Judgment Case Statement

           case $变量名 in        条件1)         分支1;;        条件2）          分支2;;        默认条件 *)           默认分支;;         esac                    每个条件后面跟  ）结尾 每个分支后面以 ;; 结束 例子             写一个能判断yes/no的脚本,(大小写均能识别，yes九种可能，no四种可能)、                      #!/bin/bash        read -p "请输入yes|no: " q        case $q in         [Yy][Ee][Ss]|[Yy])        echo "yes";;        [Nn][Oo])        echo "no";;             *)        echo "请输入正确的格式"        esac

   Three. For loop

   Execution mechanism: Assigns the element in the list to the "variable name" in turn; The loop body is executed once each assignment; Until the elements in the list are exhausted, the loop ends
   For variable name in list;
   Loop body
   Done

   Example 1 calculates the sum of 1 to 10 of all positive integers using a for loop
   #!/bin/bash
   Let S=0
   For-N in echo {1..10};d o
   S=$[$s + $n]
   Echo $s
   Done
   Example 2 printing a 99 multiplication table with a for loop
   #!/bin/bash
   For i in {1..9};d o
   For n in seq 1 $i ;d o
   Echo-n-E "$i" x "$n =$[i*n]"
   Done
   Echo
   Done

   （每一个for要对应一个done）

The use of if,case,for in shell scripts