exit 、break、continue 三者区别 在此篇:https://www.jianshu.com/p/496c9d9f1b88

1、for 循环格式

fro 变量名 in 列表
do 

    循环体

done

2、for循环举例

示例（1）for循环定义列表演示

[root@node3 /server/scripts]# cat for1.sh 
#!/usr/bin/bash

for var in file1 file2 file3
do 

    echo "this is $var"

done
[root@node3 /server/scripts]# sh for1.sh 
this is file1
this is file2
this is file3
[root@node3 /server/scripts]# 

示例（2）for循环定义列表演示

[root@node3 /server/scripts]# cat for2.sh 
#!/usr/bin/bash

for var in file1 file2 file3
do 

    echo "this is 123"

done
[root@node3 /server/scripts]# sh for2.sh 
this is 123
this is 123
this is 123
[root@node3 /server/scripts]# 

示例（3）for循环定义列表演示

[root@node3 /server/scripts]# cat for3.sh 
#!/bin/bash

for var in file1 "file2 file3" file4 "hello word"
do
echo "this is $var"
done
[root@node3 /server/scripts]# sh for3.sh 
this is file1
this is file2 file3
this is file4
this is hello word
[root@node3 /server/scripts]# 

示例（4）for循环定义列表演示

[root@node3 /server/scripts]# cat for4.sh 
#!/bin/bash

for var in file1 file\'2 file\'s
do 
echo "var is $var"

done
[root@node3 /server/scripts]# sh for4.sh 
var is file1
var is file'2
var is file's
[root@node3 /server/scripts]# 

示例（5）for循环定义列表演示

[root@node3 /server/scripts]# cat for5.sh 
#!/bin/bash
list="file1 file2 file3"

for var in $list 
do 
echo "var is $var"

done
[root@node3 /server/scripts]# sh for5.sh
var is file1
var is file2
var is file3
[root@node3 /server/scripts]# 

示例（6）IFS 定义for循环分隔符演示

[root@node3 /server/scripts]# cat for6.sh 
#!/bin/bash

#默认for循环时以空格作为分隔符
#修改IFS变量，可以控制for循环的分隔符

IFS=$'\n' #以回车作为分隔符

for i in `cat /etc/hosts` #使用文件方式读入列表
do
    echo "$i"
    sleep 1 
done
[root@node3 /server/scripts]# sh for6.sh 
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
172.16.1.5      lb01
172.16.1.6      lb02
172.16.1.7      web01
172.16.1.8      web02
172.16.1.31     nfs01
172.16.1.41     backup
172.16.1.51     db01 db01.etiantian.org
172.16.1.61     m01
[root@node3 /server/scripts]# 

示例（7）IFS 定义for循环分隔符演示

[root@node3 /case/scripts/for]# cat for7.sh 
#!/bin/bash
IFS=:   #冒号做分隔符


list=$(head -1 /etc/passwd) #使用文件读入列表

for i in $list
do
    echo $i
    sleep 1
done
[root@node3 /case/scripts/for]# sh for7.sh 
root
x
0
0
root
/root
/bin/bash
[root@node3 /case/scripts/for]#

示例（8）一种特殊（C语言方式）的使用for循环演示

[root@node3 /server/scripts]# cat for8.sh 
#!/bin/bash

for ((i=1;i<=10;i++)) 

do 

    echo num is $i 
done
[root@node3 /server/scripts]# sh for8.sh 
num is 1
num is 2
num is 3
num is 4
num is 5
num is 6
num is 7
num is 8
num is 9
num is 10

[root@node3 /server/scripts]# 

示例（9）for循环自增自减运算

[root@node3 /server/scripts]# cat for9.sh 
#!/usr/bin/bash

for (( i=1,j=10;i<=10,j>=1;i++,j-- ))
do
    echo num is $i +  $j = $[ $i + $j ]
done


[root@node3 /server/scripts]# sh for9.sh 
num is 1 + 10 = 11
num is 2 + 9 = 11
num is 3 + 8 = 11
num is 4 + 7 = 11
num is 5 + 6 = 11
num is 6 + 5 = 11
num is 7 + 4 = 11
num is 8 + 3 = 11
num is 9 + 2 = 11
num is 10 + 1 = 11
[root@node3 /server/scripts]# 

示例（10） for自增自减运算

[root@node3 /case/scripts/for]# cat for9.sh 
#!/bin/bash
a=0
b=10
for i in {1..9}
do
    let a++;
    let b--;
  echo num is $a - $b
done
[root@node3 /case/scripts/for]# sh for9.sh 
num is 1 - 9
num is 2 - 8
num is 3 - 7
num is 4 - 6
num is 5 - 5
num is 6 - 4
num is 7 - 3
num is 8 - 2
num is 9 - 1
[root@node3 /case/scripts/for]# 

示例（11）shell 并发执行

[root@node3 /case/scripts/for]# cat for10.sh 
#!/bin/bash

#批量检测主机是否存活

>ip.txt

for ip in {1..254} #列表的生成方式
do
     {
    addr=10.0.0.$ip

    ping -c 1 $addr &>/dev/null
    if [ $? -eq 0 ];then
        echo $addr | tee -a ip.txt
    fi
    }&
done

    wait
 echo "Get IP Is Finsh!!"
[root@node3 /case/scripts/for]# sh for10.sh 
10.0.0.202
10.0.0.200
10.0.0.201
10.0.0.254
Get IP Is Finsh!!
[root@node3 /case/scripts/for]#cat ip.txt 
10.0.0.200
10.0.0.201
10.0.0.202
10.0.0.254

示例（11）for 嵌套循环

[root@node3 /case/scripts/for]# cat for12.sh 

#!/usr/bin/bash

#探测多个主机的多个不同端口是否存在

> all.txt

#1.遍历ip地址
for ip in $(cat ip.txt)
do
    #2.遍历port文件循环
    for port in $(cat port.txt)
    do
        {
        nc -vz -w 1 $ip $port &>/dev/null
        if [ $? -eq 0 ];then
            echo "$ip $port" | tee -a all.txt
        fi
       }&
    done

    wait

done
[root@node3 /case/scripts/for]# sh for12.sh 
10.0.0.200 80
10.0.0.200 22
10.0.0.201 22
10.0.0.201 80
10.0.0.202 22
[root@node3 /case/scripts/for]# cat all.txt 
10.0.0.200 80
10.0.0.200 22
10.0.0.201 22
10.0.0.201 80
10.0.0.202 22
[root@node3 /case/scripts/for]#