shell脚本之基础练习题（批量创建用户、99乘法表、检查软件是否安装、解决DOS攻击...）

1、获取随机字符串或数字

方法一：

 [root@centos ~]# vim random.sh
#!/bin/bash
function print_random() {
    for i in {1..10};
    do
        echo -e "$i \t $RANDOM"
    done
}
print_random

[root@centos ~]# sh random.sh

方法二：date随机数法

[root@centos ~]# vim date.sh
#!/bin/bash
a=`date +%s%N`
echo $a
[root@centos ~]# sh date.sh

方法三：通过内部系统变量

[root@centos ~]# echo $RANDOM
5173
[root@centos ~]# echo $RANDOM
9792

2、定义一个颜色输出字符串函数

[root@centos ~]# vim color.sh
#!/bin/bash

color(){
if [ $1 == "red" ]
then
        echo -e "\033[31m$2\033[0m"
elif [ $1 == "green" ]
then
         echo -e "\033[32m$2\033[0m"
elif [ $1 == "blue" ]
then
        echo -e "\033[36m$2\033[0m"
fi
}


color green "绿色"
color red "红色"
[root@centos ~]# sh color.sh
绿色
红色

关于shell脚本字体颜色拓展

3、批量创建用户

#！/bin/bash
read -p "please input passwd:" PASSWD
for UNAME in `cat file4`
do
    id $UNAME &> /dev/null

    if [ $? -eq 0 ]
    then
        echo "the $UNAME already exist"
    else
        useradd $UNAME &> /dev/null
        echo $PASSWD | passwd --stdin $UNAME &> /dev/null
        if [ $? -eq 0 ]
        then
            echo "$UNAME create sucessful"
        else
            echo "$UNAME create failed"
        fi
    fi
done

4、检查软件包是否安装

rpm -ivh your-package                # 直接安装
rpmrpm --force -ivh your-package``.rpm # 忽略报错，强制安
[root@localhost ~]# rpm -ql tree        # 查询
[root@localhost ~]# rpm -e tree          # 卸载
[root@localhost ~]# rpm -ql tree         # 查询

#!/bin/bash
read -p "input your rpm packet name:" i
x=`rpm -qa | grep $i`
if [ $? -eq 0 ]
then
    echo "the packet already exist"
else
    `yum install $i`
fi

5、检查服务状态

方法一：
服务状态判断：
根据命令的返回值$？做判断

#!/bin/bash
`ps -ef |grep httpd |grep -v grep` &>/dev/null
if [ $? -eq 0 ]
then
    echo "httpd is up ..."
else
    echo "httpd is down ..."
fi

方法二：

netstat -tulanp |grep 80，ps -ef |grep httpd ；wc -l   #判断数字

6、检查主机存活状态

while true
do
curl 127.0.0.1  &>/dev/null
if [ $? -eq 0 ]
then
    echo " ok..."
else
    echo "not ok ..."
fi
sleep 1
done

7、监控CPU、内存和硬盘利用率

#!/bin/bash
while true
do
echo "1.查看磁盘分区
2.CPU负载
3.剩余内存
4.退出"
read -p "请输入你要执行的操作：>>>" num

PART(){
  #echo $HOSTNAME
  #fdisk l
  echo "hostname:$HOSTNAME"
  echo "system: `cat /etc/redhat-release`"
  #定义数组
  array1=(`lsblk -l |awk '/sd[a-z][0-9]/{print $1}'`)  
  array2=(`lsblk -l |awk '/sd[a-z][0-9]/{print $4}'`)  
  array3=(`lsblk -l |awk '/sd[a-z][0-9]/{print $6}'`)  
  array4=(`lsblk -l |awk '/sd[a-z][0-9]/{print $7}'`)
  #遍历数组
  num=`echo $((${#array1[@]}-1))`
  for i in `seq 0 $num`  #i=0
  do
cat <<EOF
 ---------${array1[$i]}-----------
 path: ${array1[$i]}
 size: ${array2[$i]}
 file_os: ${array3[$i]}
 mount_on：${array4[$i]}
EOF
done
}

case $num in
   1)
   PART
   #echo "parting...."
   ;;
   2)
   echo "loading..."
   ;;
   3)
   echo "mem...."
   ;;
   4)
   exit 0
   ;;
   *)
   print "please input true list..."
esac
   
done 

8、批量主机磁盘利用率监控

[root@centos ~]# lsblk -l   #磁盘利用率
NAME MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda    8:0    0   20G  0 disk
sda1   8:1    0  200M  0 part /boot
sda2   8:2    0   10G  0 part /
sda3   8:3    0    2G  0 part [SWAP]
sr0   11:0    1  3.7G  0 rom  /media

[root@centos ~]# df -h  #查看硬盘信息
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda2       9.8G  952M  8.3G  11% /
tmpfs           491M     0  491M   0% /dev/shm
/dev/sda1       190M   30M  150M  17% /boot
/dev/sr0        3.7G  3.7G     0 100% /media

df -h:查看硬盘信息
sed ‘1d’:删除第一行
awk ‘{print $5}’:打印第5列
sed ‘s/%//g’ :将%替换成空，g是全局的意思。
sed -n 1p：显示修改(-n选项)的第一行
a1-4是检查磁盘分区信息

a1=$(df -h|sed '1d'|awk '{print $5}'|sed 's/%//g'|sed -n 1p)  
a2=$(df -h|sed '1d'|awk '{print $5}'|sed 's/%//g'|sed -n 2p)  
a3=$(df -h|sed '1d'|awk '{print $5}'|sed 's/%//g'|sed -n 3p)  
a4=$(df -h|sed '1d'|awk '{print $5}'|sed 's/%//g'|sed -n 4p)

b1-4是把分区名过滤出来

b1=$(df -h|sed 1d|awk '{print $1}'|sed -n 1p)  
b2=$(df -h|sed 1d|awk '{print $1}'|sed -n 2p)  
b3=$(df -h|sed 1d|awk '{print $1}'|sed -n 3p)  
b4=$(df -h|sed 1d|awk '{print $1}'|sed -n 4p)

当前日期(年-月-日 时:分:秒)
DAY=$(date +%F\ %T)

#判断使用率，大于(-gt)80就记录日志.
if [ $a1 -gt 89 ];then  
     echo "$DAY $b1 would be near 80% !" >> /var/log/check_HD.log  
if [ $a2 -gt 89 ];then  
    echo "$DAY $b21 would be near 80% !" >> /var/log/check_HD.log  
if [ $a3 -gt 89 ];then  
     echo "$DAY $b3 would be near 80% !" >> /var/log/check_HD.log  
if [ $a4 -gt 89 ];then  
    echo "$DAY $b4 would be near 80% !" >> /var/log/check_HD.log  
fi 
fi
fi 
fi

9、检查网站可用性

#!/bin/bash

function usage(){
echo $"usage:$0 url"
exit 1
}

function check_url() {

wget --spider -q -o /dev/null --tries=1 -T 5 $1
if [ $? -eq 0 ]
then
echo "$1 is yes."
exit 0
else
echo "$1 is fail."
exit 1
fi
}

10、用source 执行脚本和用bash 执行 Shell 脚本的区别是什么？

bash执行脚本，在脚本执行完毕退出后，脚本定义的资源将被回收
source执行的脚本，脚本定义的资源将会加载到其父进程

11、定义变量内容，不加引号、单引号、双引号、反引号有什么区别？

[root@localhost test]# a=linux
[root@localhost test]# echo $a
linux
[root@localhost test]# b="$a is"
[root@localhost test]# echo $b
linux is
[root@localhost test]# b='$a is'
[root@localhost test]# echo $b
$a is
[root@localhost test]# c=`date`
[root@localhost test]# echo $c
Mon Jul 6 15:56:32 CST 2020
不加引号：用于一些简单字符数字的定义，与双引号类似
单引号：强引，不管里面是否有变量或者其他表达都是原样子输出
双引号：如果其定义变量的时候使用双引号，则里面的变量或者函数会通过解析，解析完成后再输出，而不是把双引号中的变量名以及命令原样子输出
反引号：一般用于引用命令，执行的时候命令会被执行

12、编写shell脚本，计算1~100的和

sum=0
for i in {1..100}
do
    let sum=sum+$i
done
echo $sum

13、编写shell脚本，输入一个数字n并计算1~n的和

read  -p "please input a number:" n
sum=0
for i in $(seq 1 $n)
do
    let sum=$(($sum+$i))
done
echo $sum

14、编写shell脚本，批量建立用户user_00、user_01…user_99

for i in {00..99}
do
    useradd user_$i
    echo 111111 |passwd --stdin user_$i
done

15、编写shell脚本，实现两个变量之间的加减乘除运算

read -p "please input one number:" m
read -p "please input another number:" n
let a=$(($m+$n))
let b=$(($m-$n))
let c=$(($m*$n))
let d=$(($m/$n))
echo "相加:$a"
echo "相减:$b"
echo "相乘:$c"
echo "相除:$d"

16、利用bash for循环打印下面这句话中字母数不大于6的单词

I am clsn Welcome to my blog http://blog.znix.top

a="I am clsn Welcome to my blog http://blog.znix.top"
echo $a |awk -F "[^a-zA-Z]" '{for (i=1;i<=NF;i++){if (0$i) && length($i)<6){print $i}}}'

17、请用shell或Python编写一个正（或长）方形，接收用户输入的数字

read -p "please input the length:" b
read -p "please input the width:" a
for i in `seq 1 $a`
do
    for j in `seq 1 $b`
    do
        echo -n "*"
    done
    echo ""
done

18、写一个Shell脚本解决DOS攻击生产案例

while true
do
    #netstat -tan |grep ESTABLISHED |awk -F "[ :]+" '{array[$6]++}END{for (i in array) print i,array[i]}' >netstat.txt
    netstat -tan |grep SYS_RECV |awk -F "[ :]+" '{array[$6]++}END{for (i in array) print i,array[i]}' >netstat.txt
    while read line
    do
        echo $line
        n=`echo $line |awk '{print $2}'`
        m=`echo $line |awk '{print $1}'`
        if (($n>5))
        then
            iptables -t filter -I INPUT -s $m -j REJECT
        fi
        echo $n
    done < netstat.txt
    sleep 2
done

19、用shell处理以下内容

1、按单词出现频率降序排序！
　　2、按字母出现频率降序排序！
the squid project provides a number ofresources to assist users design implement and support squid installations.Please browse the documentation and support sections for more infomation byoldboy training

word="the squid project provides a number ofresources to assist users design implement and support squid installations.Please browse the documentation and support sections for more infomation byoldboy training"

awk '{for (i=1;i<=length($0);i++){if (substr($0,i,1)~/[a-z]/) array[substr($0,i,1)]++}} END{for (i in array) print i,array[i]}' word |sort -nrk2

20、九九乘法表

for i in `seq 1 9`
do
    for j in `seq 1 $i`
    do
        echo -ne "$i*$j=$(($i*$j))\t"
    done
    echo ""
done