Shell脚本编写及常见面试题

2023-08-14 09:22:10

 

注意事项

1）开头加解释器：#!/bin/bash

2）语法缩进，使用四个空格；多加注释说明。

3）命名建议规则：变量名大写、局部变量小写，函数名小写，名字体现出实际作用。

4）默认变量是全局的，在函数中变量local指定为局部变量，避免污染其他作用域。

5）有两个命令能帮助我调试脚本：set -e 遇到执行非0时退出脚本，set-x 打印执行过程。

6）写脚本一定先测试再到生产上。

本章目录：

Shell脚本编写及常见面试题

12.1 获取随机字符串或数字

获取随机8位字符串：

方法1：

# echo $RANDOM |md5sum |cut -c 1-8

471b94f2

方法2：

# openssl rand -base64 4

vg3BEg==

方法3：

# cat /proc/sys/kernel/random/uuid |cut -c 1-8

ed9e032c
 

获取随机8位数字：

方法1：

# echo $RANDOM |cksum |cut -c 1-8

23648321

方法2：

# openssl rand -base64 4 |cksum |cut -c 1-8

38571131

方法3：

# date +%N |cut -c 1-8

69024815
 

cksum：打印CRC效验和统计字节

12.2 定义一个颜色输出字符串函数

方法1：

function echo_color() {

    if [ $1 == "green" ]; then

        echo -e "\033[32;40m$2\033[0m"

    elif [ $1 == "red" ]; then

        echo -e "\033[31;40m$2\033[0m"

    fi

}

方法2：

function echo_color() {

    case $1 in

        green)

            echo -e "\033[32;40m$2\033[0m"

            ;;

        red)

            echo -e "\033[31;40m$2\033[0m"

            ;;

        *)

            echo "Example: echo_color red string"

    esac

}

使用方法：echo_color green "test"
 

function关键字定义一个函数，可加或不加。

12.3 批量创建用户

#!/bin/bash

DATE=$(date +%F_%T)

USER_FILE=user.txt

echo_color(){

    if [ $1 == "green" ]; then

        echo -e "\033[32;40m$2\033[0m"

    elif [ $1 == "red" ]; then

        echo -e "\033[31;40m$2\033[0m"

    fi

}

# 如果用户文件存在并且大小大于0就备份

if [ -s $USER_FILE ]; then

    mv $USER_FILE ${USER_FILE}-${DATE}.bak

    echo_color green "$USER_FILE exist, rename ${USER_FILE}-${DATE}.bak"

fi

echo -e "User\tPassword" >> $USER_FILE

echo "----------------" >> $USER_FILE

for USER in user{1..10}; do

    if ! id $USER &>/dev/null; then

        PASS=$(echo $RANDOM |md5sum |cut -c 1-8)

        useradd $USER

        echo $PASS |passwd --stdin $USER &>/dev/null

        echo -e "$USER\t$PASS" >> $USER_FILE

        echo "$USER User create successful."

    else

        echo_color red "$USER User already exists!"

    fi

done
 

12.4 检查软件包是否安装

#!/bin/bash

if rpm -q sysstat &>/dev/null; then

    echo "sysstat is already installed."

else

    echo "sysstat is not installed!"

fi
 

12.5 检查服务状态

#!/bin/bash

PORT_C=$(ss -anu |grep -c 123)

PS_C=$(ps -ef |grep ntpd |grep -vc grep)

if [ $PORT_C -eq 0 -o $PS_C -eq 0 ]; then

    echo "内容" | mail -s "主题" dst@example.com

fi
 

12.6 检查主机存活状态

方法1：将错误IP放到数组里面判断是否ping失败三次

#!/bin/bash

IP_LIST="192.168.18.1 192.168.1.1 192.168.18.2"

for IP in $IP_LIST; do

    NUM=1

    while [ $NUM -le 3 ]; do

        if ping -c 1 $IP > /dev/null; then

            echo "$IP Ping is successful."

            break

        else

            # echo "$IP Ping is failure $NUM"

            FAIL_COUNT[$NUM]=$IP

            let NUM++

        fi

    done

    if [ ${#FAIL_COUNT[*]} -eq 3 ];then

        echo "${FAIL_COUNT[1]} Ping is failure!"

        unset FAIL_COUNT[*]

    fi

done
 

方法2：将错误次数放到FAIL_COUNT变量里面判断是否ping失败三次

#!/bin/bash

IP_LIST="192.168.18.1 192.168.1.1 192.168.18.2"

for IP in $IP_LIST; do

    FAIL_COUNT=0

    for ((i=1;i<=3;i++)); do

        if ping -c 1 $IP >/dev/null; then

            echo "$IP Ping is successful."

            break

        else

            # echo "$IP Ping is failure $i"

            let FAIL_COUNT++

        fi

    done

    if [ $FAIL_COUNT -eq 3 ]; then

        echo "$IP Ping is failure!"

    fi

done
 

方法3：利用for循环将ping通就跳出循环继续，如果不跳出就会走到打印ping失败

#!/bin/bash

ping_success_status() {

    if ping -c 1 $IP >/dev/null; then

        echo "$IP Ping is successful."

        continue

    fi

}

IP_LIST="192.168.18.1 192.168.1.1 192.168.18.2"

for IP in $IP_LIST; do

    ping_success_status

    ping_success_status

    ping_success_status

    echo "$IP Ping is failure!"

done
 

12.7 监控CPU、内存和硬盘利用率

1）CPU

借助vmstat工具来分析CPU统计信息。

#!/bin/bash

DATE=$(date +%F" "%H:%M)

IP=$(ifconfig eth0 |awk -F '[ :]+' '/inet addr/{print $4}')  # 只支持CentOS6

MAIL="example@mail.com"

if ! which vmstat &>/dev/null; then

    echo "vmstat command no found, Please install procps package."

    exit 1

fi

US=$(vmstat |awk 'NR==3{print $13}')

SY=$(vmstat |awk 'NR==3{print $14}')

IDLE=$(vmstat |awk 'NR==3{print $15}')

WAIT=$(vmstat |awk 'NR==3{print $16}')

USE=$(($US+$SY))

if [ $USE -ge 50 ]; then

    echo "

    Date: $DATE

    Host: $IP

    Problem: CPU utilization $USE

    " | mail -s "CPU Monitor" $MAIL

fi
 

2）内存

#!/bin/bash

DATE=$(date +%F" "%H:%M)

IP=$(ifconfig eth0 |awk -F '[ :]+' '/inet addr/{print $4}')

MAIL="example@mail.com"

TOTAL=$(free -m |awk '/Mem/{print $2}')

USE=$(free -m |awk '/Mem/{print $3-$6-$7}')

FREE=$(($TOTAL-$USE))

# 内存小于1G发送报警邮件

if [ $FREE -lt 1024 ]; then

    echo "

    Date: $DATE

    Host: $IP

    Problem: Total=$TOTAL,Use=$USE,Free=$FREE

    " | mail -s "Memory Monitor" $MAIL

fi
 

3）硬盘

#!/bin/bash

DATE=$(date +%F" "%H:%M)

IP=$(ifconfig eth0 |awk -F '[ :]+' '/inet addr/{print $4}')

MAIL="example@mail.com"

TOTAL=$(fdisk -l |awk -F'[: ]+' 'BEGIN{OFS="="}/^Disk \/dev/{printf "%s=%sG,",$2,$3}')

PART_USE=$(df -h |awk 'BEGIN{OFS="="}/^\/dev/{print $1,int($5),$6}')

for i in $PART_USE; do

    PART=$(echo $i |cut -d"=" -f1)

    USE=$(echo $i |cut -d"=" -f2)

    MOUNT=$(echo $i |cut -d"=" -f3)

    if [ $USE -gt 80 ]; then

        echo "

        Date: $DATE

        Host: $IP

        Total: $TOTAL

        Problem: $PART=$USE($MOUNT)

        " | mail -s "Disk Monitor" $MAIL

    fi

done
 

12.8 批量主机磁盘利用率监控

前提监控端和被监控端SSH免交互登录或者密钥登录。

写一个配置文件保存被监控主机SSH连接信息，文件内容格式：IP User Port

#!/bin/bash

HOST_INFO=host.info

for IP in $(awk '/^[^#]/{print $1}' $HOST_INFO); do

    USER=$(awk -v ip=$IP 'ip==$1{print $2}' $HOST_INFO)

    PORT=$(awk -v ip=$IP 'ip==$1{print $3}' $HOST_INFO)

    TMP_FILE=/tmp/disk.tmp

    ssh -p $PORT $USER@$IP 'df -h' > $TMP_FILE

    USE_RATE_LIST=$(awk 'BEGIN{OFS="="}/^\/dev/{print $1,int($5)}' $TMP_FILE)

    for USE_RATE in $USE_RATE_LIST; do

        PART_NAME=${USE_RATE%=*}

        USE_RATE=${USE_RATE#*=}

        if [ $USE_RATE -ge 80 ]; then

            echo "Warning: $PART_NAME Partition usage $USE_RATE%!"

        fi

    done

done
 

12.9 检查网站可用性

1）检查URL可用性

方法1：

check_url() {

    HTTP_CODE=$(curl -o /dev/null --connect-timeout 3 -s -w "%{http_code}" $1)

    if [ $HTTP_CODE -ne 200 ]; then

        echo "Warning: $1 Access failure!"

    fi

}

方法2：

check_url() {

if ! wget -T 10 --tries=1 --spider $1 >/dev/null 2>&1; then

#-T超时时间，--tries尝试1次，--spider爬虫模式

        echo "Warning: $1 Access failure!"

    fi

}

使用方法：check_url www.baidu.com
 

2）判断三次URL可用性

思路与上面检查主机存活状态一样。

方法1：利用循环技巧，如果成功就跳出当前循环，否则执行到最后一行

#!/bin/bash

check_url() {

    HTTP_CODE=$(curl -o /dev/null --connect-timeout 3 -s -w "%{http_code}" $1)

    if [ $HTTP_CODE -eq 200 ]; then

        continue

    fi

}

URL_LIST="www.baidu.com www.agasgf.com"

for URL in $URL_LIST; do

    check_url $URL

    check_url $URL

    check_url $URL

    echo "Warning: $URL Access failure!"

done

方法2：错误次数保存到变量

#!/bin/bash

URL_LIST="www.baidu.com www.agasgf.com"

for URL in $URL_LIST; do

    FAIL_COUNT=0

    for ((i=1;i<=3;i++)); do

        HTTP_CODE=$(curl -o /dev/null --connect-timeout 3 -s -w "%{http_code}" $URL)

        if [ $HTTP_CODE -ne 200 ]; then

            let FAIL_COUNT++

        else

            break

        fi

    done

    if [ $FAIL_COUNT -eq 3 ]; then

        echo "Warning: $URL Access failure!"

    fi

done

方法3：错误次数保存到数组

#!/bin/bash

URL_LIST="www.baidu.com www.agasgf.com"

for URL in $URL_LIST; do

    NUM=1

    while [ $NUM -le 3 ]; do

        HTTP_CODE=$(curl -o /dev/null --connect-timeout 3 -s -w "%{http_code}" $URL)

        if [ $HTTP_CODE -ne 200 ]; then

            FAIL_COUNT[$NUM]=$IP  #创建数组，以$NUM下标，$IP元素

            let NUM++

        else

            break

        fi

    done

    if [ ${#FAIL_COUNT[*]} -eq 3 ]; then

        echo "Warning: $URL Access failure!"

        unset FAIL_COUNT[*]    #清空数组

    fi

done
 

12.10 检查MySQL主从同步状态

#!/bin/bash

USER=bak

PASSWD=123456

IO_SQL_STATUS=$(mysql -u$USER -p$PASSWD -e 'show slave status\G' |awk -F: '/Slave_.*_Running/{gsub(": ",":");print $0}')  #gsub去除冒号后面的空格

for i in $IO_SQL_STATUS; do

    THREAD_STATUS_NAME=${i%:*}

    THREAD_STATUS=${i#*:}

    if [ "$THREAD_STATUS" != "Yes" ]; then

        echo "Error: MySQL Master-Slave $THREAD_STATUS_NAME status is $THREAD_STATUS!"

    fi

done
上一篇：牛客练习赛7 E 珂朵莉的数列（树状数组+爆long long解决方法）


下一篇：配置中心Client端