shell脚本(三)

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一. 使用if条件语句

案例：

单分支IF

1).根分区已用空间>80%则报警，否则不执行任何操作

#!/bin/bash

echo "===Check disk usage...==="

DISKU=df -h|awk '/vda1/{print $5}'|awk -F% '{print $1}'

if [ $DISKU -gt 10 ] ; then

echo "warning,Disk vda1 is over 90 usages....."

echo "warning,Disk vda1 is over 90 usages....."> /var/log/diskusage.log

else

echo "disk vda1 is normal.Good luck."

fi

2).执行脚本时指定IP，结果为ping该主机，若通，则显示up，否则显示down

#!/bin/bash

ping -c2 172.18.199.10 &>> /dev/null

if [ $? -eq 0 ]

then

echo "The IP $1 is up."

else

echo "The IP $1 is down."

fi

练习

#!/bin/bash

#writed by jason.check ip.

clear

echo ===Check IP up or down===

read -p "Please input your IP address:" CKIP

if [[ "$CKIP" =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]] ; then

    echo "nice ip $CKIP"

    ping -c1 -w 1 $CKIP &> /dev/null

        if [ $? -eq 0 ] ; then

            echo "The ip $CKIP is up."

        else

            echo "The ip $CKIP is down."

        fi

else

    echo "wrong ip $CKIP."

    echo "error,input wrong."

fi

3).判断httpd是否已经启动，若已启动，则提示已运行，否则启动httpd服务

systemctl status httpd

if [ $? -eq 0 ]

then

echo “Service httpd is running.”

else

Systemctl start  httpd

fi

双分支IF

4).判断/tmp目录下是否有win目录，若不存在则创建目录，存在不执行任何操作

#!/bin/bash

if [ ! -e /tmp/win ] ;then

echo "To create dir win"

mkdir /tmp/win

elif [ -f /tmp/win ] ;then

echo "To del win file"

rm -rf /tmp/win

echo "To create dir win"

mkdir /tmp/win

else

echo "此目录win已经存在了。"

fi

多分支示例：

脚本可互动输入分数，并判断分数在90-100之间，判断为优秀，60-89之间为合格，59-40以下其他为不及格努力；39以下复读,其它输入为非法输入。

#!/bin/bash

echo "=======Test========"

read -p "请输入你的成绩" Source

if [ $Source -gt 100 ] ; then

echo "输入错误"

elif [ $Source -lt 0 ] ; then

echo "输入错误"

elif [ $Source -ge 90 ] ; then

echo "优秀"

elif [ $Source -ge 60 ] ; then

echo "及格"

elif [ $Source -ge 40 ] ; then

echo "努力"

else

echo "复读"；

fi

二、循环语句:

1、FOR循环写法

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

for i in `seq 10`

for i in {1..10}

#!/bin/bash

for i in {1..10}

do

echo “$i”

done

#!/bin/bash

for i in $*

do

echo “$i”

done

for  i in {30..39}

do

echo $i

done

vim num.txt

#!/bin/bash

for i in `cat num.txt`

do

echo “$i”

done

#!/bin/bash

ipnet='172.18.11.'

for IPaddress in {1..254}

do

ping -c 1 $ipnet$IPaddress &> /dev/null

if [ $? -eq 0 ] ; then

echo "This host $ipnet$IPaddress is up."

echo "This host $ipnet$IPaddress is up." >> /tmp/ping-18net.log

else

echo "This host $ipnet$IPaddress is down."

fi

done

echo "Net18 ping over."

#!/bin/bash

for (( i = 1; i <=9; i++ ))

do

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

do

let "chengji = i * j"

echo -n "$i*$j=$chengji "

done

echo ""

done

2、while循环写法

如：

i=1

while [ $i -lt 10 ]

do

echo $i

let i++

done

#!/bin/bash

echo "=======Test score========"

while true ;

do

read -p "请输入你的成绩: " Source

if [ "$Source" = "exit" ] ; then

  exit

elif [[ "$Source" != [0-9]* ]] ; then

echo "err,you input character."

elif [ $Source -gt 100 ] ; then

echo "输入错误"

elif [ $Source -lt 0 ] ; then

echo "输入错误"

elif [ $Source -ge 90 ] ; then

echo "优秀"

elif [ $Source -ge 60 ] ; then

echo "及格"

elif [ $Source -ge 40 ] ; then

echo "努力"

elif [ $Source -ge 0 ] ; then

echo "复读"；

else

echo "input error."

fi

done

或

#!/bin/bash

#writed by jason,fenshu.

clear

echo "====Check fenshu...===="

while true

do

    read -p "input your score:" Source

            expr $Source + 1 &>/dev/null

            if [ ! $? -eq 0 ] ; then

                echo "error,wrong.You must input number."

            elif [ "$Source" -gt 100 ] ; then

                echo "Number too big."

            elif [ "$Source" -lt 0 ] ; then

                echo "Number too small."

            elif [ "$Source" -ge 90 ] ; then

                echo "You are great."

            elif [ "$Source" -ge 60 ] ; then

                echo "You are just so so ."

            elif [ "$Source" -ge 40 ] ; then

                echo "No pass,try your best."

            elif [ "$Source" -ge 0 ] ; then

                echo "You must go home."

            else

                echo "You input err,try again."

            fi

done

或者

#!/bin/bash

echo "=======Test score========"

while true ;

do

read -p "请输入你的成绩: " Source

if [ "$Source" = "exit" ] ; then

  exit

else

if [[ "$Source" =~ ^[1-9][0-9]{0,2}$ ]] ; then

if [ $Source -gt 100 ] ; then

echo "输入错误"

elif [ $Source -lt 0 ] ; then

echo "输入错误"

elif [ $Source -ge 90 ] ; then

echo "优秀"

elif [ $Source -ge 60 ] ; then

echo "及格"

elif [ $Source -ge 40 ] ; then

echo "努力"

elif [ $Source -ge 0 ] ; then

echo "复读"；

else

echo "input number error."

fi

else

echo "error,not number."

fi

fi

done

补充

循环结构中数值增量需要与let合作，如let i++

i++ 等同于 i=i+1

i+=1 等同于 i=i+1

i+=2 i=i+2

i--  i=i-1

i-=2 i=i-2

i*=2 i=i*2

作业：用脚本完成

1.公司要求新进一批实习生，要为他们建立用户名shixi01 ---- shixi10,要求所有人的密码初始都为great123。

2.用FOR循环写九九乘法表。

3.用for及while结构分别完成扫描本网段址的脚本

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分享题目：第二十三章SHELL脚本-CENTOS7.5知识-创新互联
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