Shell之三

Posted 2020-10-28

第1章 while循环语句

在编程语言中,while循环是一种控制流程的陈述,利用一个返回结果为布林值的表达式,当这个表达式的返回值为真时,则反复执行循环的条件,若表达式的返回值为假,则不在执行循环的条件

1.1 while语法:

while 条件

  do

    命令

done

1.2 while使用场景:

1.2.1 多用于创建守护进程

[[email protected] tmp]# cat test.sh

#!/bin/bash

##############################################################

# File Name: test.sh

# Version: V1.0

# Author: da ya

# Organization: [email protected]

# Created Time : 2018-03-24 19:48:06

# Description:

##############################################################

while true

  do

  echo "ok" | nc -l 81

done

[[email protected] tmp]# sh test.sh

GET / HTTP/1.1

User-Agent: curl/7.29.0

Host: 10.0.0.31:81

Accept: */*

 

GET / HTTP/1.1

User-Agent: curl/7.29.0

Host: 10.0.0.31:81

Accept: */*

1.2.2 可以创建定时任务,执行时间小于一分钟的定时任务

[[email protected] tmp]# cat test.sh

#!/bin/bash

while true       使返回值总是为真,所以会一直循环

  do

    uptime

    sleep 1

done

[[email protected] tmp]# sh test.sh

 19:48:45 up 2 days,  4:12,  4 users,  load average: 0.08, 0.04, 0.05

 19:48:46 up 2 days,  4:12,  4 users,  load average: 0.08, 0.04, 0.05

 19:48:47 up 2 days,  4:12,  4 users,  load average: 0.08, 0.04, 0.05

 19:48:48 up 2 days,  4:12,  4 users,  load average: 0.07, 0.04, 0.05

^C

1.3 while作用:

补充定时任务功能,执行小于一秒的任务

循环执行某些操作,例如水果菜单

1.4 遍历文件中的每一行:

1.4.1 方法一:

while read i

  do

    echo "$i"

done < /etc/hosts

[[email protected] scripts]# sh test.sh

127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4

::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

192.168.16.200 mirrors.aliyun.com

1.4.2 方法二:

cat /etc/hosts|while read i

  do

    echo "$i"

done

1.4.3 方法三:

exec < /etc/hosts

while read i

  do

    echo "$i"

done

获取一行中每个单词

while read i

  do

    echo "$i"

      for w in $i

        do

        echo "$w"

      done

done < /etc/hosts

第1章 循环控制脚本

1.1 示例:Break

for i in {1..5}

  do

    if [ "$i" -eq 2 ];then

      break

    fi

    echo "$i"

done

echo OK

[[email protected] scripts]# sh test.sh

1

OK

1.2 示例:continue

for i in {1..5}

  do

    if [ "$i" -eq 2 ];then

      continue

    fi

    echo "$i"

done

echo OK

[[email protected] scripts]# sh test.sh

1

3

4

5

OK

1.3 示例:exit

for i in {1..5}

  do

    if [ "$i" -eq 2 ];then

      exit

    fi

    echo "$i"

done

echo OK

[[email protected] scripts]# sh test.sh

1

第2章 shell数组

简答的说:数组就是多个变量的组合

[[email protected] scripts]# name=(jiang bo yang)

[[email protected] scripts]# echo ${name[1]}

bo

[[email protected] scripts]# echo ${name[2]}

yang

[[email protected] scripts]# unset name[1]

[[email protected] scripts]# echo ${name[1]}

 

[[email protected] scripts]# echo ${name[*]}

jiang yang

[[email protected] scripts]# echo ${name[@]}

jiang yang

[[email protected] scripts]# name[1]=bo

[[email protected] scripts]# echo ${name[@]}

jiang bo yang

第1章 shell函数

1.1 定义函数:

jiang(){

  echo nihao

}

jiang                  表示调用上面定义的函数

[[email protected] scripts]# sh test.sh

nihao

1.2 函数的扩展用法:添加一条命令

[[email protected] scripts]# source test.sh

nihao

[[email protected] scripts]# jiang

nihao

1.3 函数的传参

jiang(){

  echo nihao $1

}

daya(){

  echo buhao $1

}

jiang $1

daya $1

[[email protected] scripts]# sh test.sh 1

nihao 1

buhao 1

1.4 basename命令的用法

[[email protected] scripts]# basename /server/scripts/test.sh

test.sh

[[email protected] scripts]# basename /server/scripts/test.sh .sh     

test

第2章 shell调试技巧:

2.1 断电调试:

jiang(){

  echo nihao $1

}

daya(){

  echo buhao $1

}

jiang

exit              在可能有问题地方加上exit,不在继续向下执行脚本,缩小排查范围

daya

2.2 使用-x参数:

[[email protected] scripts]# sh -x test.sh

+ jiang

+ echo nihao

nihao

+ daya

+ echo buhao

buhao

2.3 指定调试范围:

[[email protected] scripts]# sh test.sh

nihao

+ daya

+ echo buhao

buhao

+ set +x