面试前临时抱佛脚——常见的Shell脚本面试题

1 获取随机字符串或数字

获取随机8位字符串：

Method One

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

Method Two

openssl rand -base64 4

Method Three

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

获取随机8位数字：

Method One

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

Method Two

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

Method Three

date +%N |cut -c 1-8

2 定义一个颜色输出字符串函数

Method one

#!/bin/bash

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
}

echo_color red "test"

Method Two

#!/bin/bash

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
}
echo_color red "我爱你"

function关键字定义一个函数，可加或不加。

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

4 检查软件包是否安装

[root@server shell]# cat install.sh 
#!/bin/bash
if rpm -q $1 &>/dev/null; then
    echo "$1 is already installed."
else
    echo "$1 is not installed!"
fi

5 检查主机存活状态

#!/bin/bash  
IP_LIST="172.25.6.250 172.25.6.1 172.25.6.2 114.114.114.114"
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

6 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 $4}')  # 只支持CentOS6
MAIL="[email protected]"
if ! which vmstat &>/dev/null; then
    echo "vmstat command no found, Please install procps package." 
    exit 1
fi
US=$(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 $4}')  
MAIL="[email protected]"
TOTAL=$(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 $4}')  
MAIL="[email protected]"
TOTAL=$(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

7 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

8 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
}
check_url www.baidu.com

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
}
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

9 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