c=$[$c%5] to let c= $c%5 conversion

Just learned the shell don't know how to convert, now understand a little, record under
It's better to be an addition.

  
 

   
  

  
c=$[$c+5]
   
  

  
let c=$c+5 变量c等于C加上5后在赋值给自身
   
  

  
let c+=5 就可以这样表示了
   
  

  

   
  

  
例如：
   
  

  
脚本代码如下
   
  

  
declare -i SUM=0
   
  

  
for ((J=2;J<=100;J+=2));do
   
  

  
 let SUM+=$J
   
  

  
 echo $SUM
   
  

  
done
   
  

  
echo $SUM
   
  

  

   
  

  
执行结果如下： 
   
  

  
+ declare -i SUM=0
   
  

  
+ (( J=2 )) #首先赋值J=2
   
  

  
+ (( J<=100 )) #J小于100就继续执行
   
  

  
+ let SUM+=2 #计算SUM的值，SUM+=变量J，J此时等于2，变量SUM等于SUM加上2后在赋值给自身
   
  

  
+ echo 2
   
  

  
2 #此时SUM等于2
   
  

  
+ (( J+=2 )) #现在J=2了，然后J+2后在往自身赋值，就变成4了
   
  

  
+ (( J<=100 )) #J小于100就继续执行
   
  

  
+ let SUM+=4 #SUM经过上轮计算现在等于2,SUM+4后在往自身赋值就变成6了
   
  

  
+ echo 6
   
  

  
6 #此时SUM等于6
   
  

  
+ (( J+=2 )) #现在J=4了，然后J+2后在往自身赋值，就变成6了
   
  

  
+ (( J<=100 )) #J小于100就继续执行
   
  

  
+ let SUM+=6 #SUM经过上轮计算现在等于6,SUM+6后在往自身赋值就变成12了
   
  

  
+ echo 12
   
  

  
12 #最终显示12
  
 

Same in +-*/% are common
About the + + value problem

  
 

   
  

  
代码如下
   
  

  

   
  

  
declare -i SUM=0
   
  

  
for ((J=2;J<=100;J++));do
   
  

  
 let SUM+=$J
   
  

  
 echo $SUM
   
  

  
done
   
  

  
echo $SUM
   
  

  

   
  

  
事例如下
   
  

  
+ declare -i SUM=0
   
  

  
+ (( J=2 )) #首先赋值J =2
   
  

  
+ (( J<=100 )) #J小于100就继续执行
   
  

  
+ let SUM+=2 #计算SUM的值, the sum+= variable j,j is equal to 2 at this time, the variable sum equals sum plus 2 is assigned to itself
   
  

  
+ echo 2
   
  

  
2 #此时SUM等于2
   
  

  
+ (( J++ )) #现在J = 2, and then J + + in the self-assignment, that is, adding 1 to itself, it becomes 3.
   
  

  
+ (( J<=100 )) #J小于100就继续执行
   
  

  
+ let SUM+=3 #SUM经过上轮计算现在等于2, after sum+3, the assignment to itself becomes 5.
   
  

  
+ echo 5
   
  

  
5 #此时SUM等于5
   
  

  
+ (( J++ )) #现在J = 3, and then J + + in the self-assignment, that is, adding 1 to itself, it becomes 4.
   
  

  
+ (( J<=100 )) #J小于100就继续执行
   
  

  
+ let SUM+=4 #SUM经过上轮计算现在等于2, after sum+4, the assignment to itself becomes 9.
   
  

  
+ echo 9 
   
  

  
9 #此时SUM等于5
   
  

  
+ (( J++ )) #现在J = 4, and then J + + in the self-assignment, that is, adding 1 to itself, it becomes 5.
   
  

  
+ (( J<=100 )) #J小于100就继续执行
   
  

  
+ let SUM+=5 #SUM经过上轮计算现在等于9, after sum+5, the assignment to itself becomes 14.
   
  

  
+ echo 14
   
  

  
14 #此时SUM等于14
  
 

This method can only be applied to--the rest cannot be executed.



From for notes (Wiz)

c=$[$c%5] to let c= $c%5 conversion