Shell Script Loop statement--for loop

Learning scripts is to facilitate our operations, and for OPS, there is a lot of work that needs to be done repeatedly, such as when we manage user accounts we need to create and delete user accounts in bulk. At this time if using the system comes with the Useradd or Userdel to operate, it can only be a mechanical one of the creation, one of the deletion. Then we can consider writing a program, let it automate to create. At this point, our loop execution concept comes out. A loop is a procedure that allows a program to perform related operations repeatedly, in a certain condition, until the loop condition is met.

Common categories of circular statements:
1,for statements
2,while statements
3,until statements

The loop body consists of two parts:
1, the entry condition of the loop
2, the exit condition of the loop

Number of Cycles:
1, pre-known for statement
2, prior unknown while, until statement

Syntax format:
For variable name in list;
Loop body
Done

Loop execution mechanism: assigns the element in the list to the variable name sequentially, executes the loop body once each assignment, until the element in the list is exhausted and the loop ends

List Generation Method:
(1) Give the list directly
(2) List of integers:
(a) {start: End} such as: {1.. 10}
(b) $ (SEQ [start [step]] end) such as: ' SEQ 1 2 100 ' represents all odd numbers between 1-100
(3) Returns a list of commands (command) such as: ' Ls/etc '
(4) using glob, such as: *.sh
(5) variable reference; [email protected], $*

For loop Application Example:

1, computes the and of all positive integers between 1-100

#!/bin/bash

#Author: Wangjun
#Contact qq:183530300
#Version: 1.0
#Create TIME:2016-08-17 16:53:28
#Description: 1-100 all positive integer ' s sum

Declare-i sum=0

For I in {1..100};d o
Let sum+= $I
Done
echo "1-100 all positive integer ' sum: $sum"

2, automatic scanning 1-254 network segment of all hosts, statistics on the number of online hosts and the number of non-online hosts

#!/bin/bash

#Author: Wangjun
#Contact qq:183530300
#Version: 1.0
#Create TIME:2016-08-17 11:25:37
#Description:p ing all hosts and count the number

Declare-i online=0
Declare-i offline=0

For host in ' seq 254 ';d o
Ping-c 1-w 1 10.1.250. $host &>/dev/null && echo "10.1.250. $host is Online" && let online= $online +1 | | Let offline++
Done
echo "Online hosts number: $online"
echo "Offline hosts number: $offline"

3, generate 10 random numbers and find the maximum random number and minimum random number

#!/bin/bash

#Author: Wangjun
#Contact qq:183530300
#Version: 1.0
#Create TIME:2016-08-17 17:27:45
#Description: Random number comparative

Minrandom= $RANDOM
Maxrandom= $minrandom
Echo $minrandom

For I in {1..9};d o
rd= $RANDOM
Echo $RD
if [[$RD-gt $maxrandom]];then
Maxrandom= $RD
elif [[$RD-lt $minrandom]];then
Minrandom= $RD
Fi
Done
echo "Minrandom is: $minrandom"
echo "Maxrandom is: $maxrandom"

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4, Print 99 multiplication table (first edition)

#!/bin/bash

#Author: Wangjun
#Contact qq:18353030
#Version: 1.0
#Create time:2016-08-16 13:07:40
#Description: Multiplication table

For Row in {1..9};d o
For Column in ' seq $Row ';d o
Echo-ne "${column}x${row}=$[$Row * $Column]\t"
Done
Echo
Done

5, Print 99 multiplication Table (second edition)

#!/bin/bash

#Author: Wangjun
#Contact qq:183530300
#Version: 1.0
#Create time:2016-08-18 11:35:16
#Description: Multiplication table

For ((row=1;row<=9;row++));d o
For ((column=1;column<= $row; column++));d o
Echo-ne "${column}x${row}=$[${column}*${row}]\t"
Done
Echo
Done

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Shell Script Loop statement--for loop