练习8

1.每隔3秒到系统上获取已经登录的用户的信息；如果发现用户hacker登录，则将登录时间和主机记录于日志/var/log/login.log中，并退出脚本

#!/bin/bash
>/var/log/login.log
until false;do
   if who |grep "^hacker\>" &>/dev/null;then
     who|grep "^hacker\>">/var/log/login.log
         break
   fi
           sleep 3
done

2.随机生成10以内的数字，实现猜字游戏，提示比较大小，相等则退出

[root@centos7 ~]# vim test8.sh 
#!/bin/bash
read -p "please input compare num:" com_num
set ran_num
ran_num=$[$RANDOM%10]
echo $ran_num
echo $com_num
[ $ran_num -eq $com_num ] && echo "equal" && exit 11
[ $ran_num -le $com_num ] && echo "less than" && exit 12
[ $ran_num -gt $com_num ] && echo "big than" && exit 13

3.用文件名做为参数，统计所有参数文件的总行数

[root@centos7 ~]# cat test9.sh 
#!/bin/bash
[ -a $1 ]||{ echo "the file is not exist,please input again";exit 10; }
[ $# -eq 0 ]&& echo "you must input a filename"&& exit 100
let sum=0
until [ $# -eq 0 ];do
        n=`wc -l<$1`&>/dev/null
        let sum+=n
        shift
done
echo sum=$sum
[root@centos7 ~]# ./test9.sh /etc/passwd test8.sh
sum=54

4.用两个以上的数字为参数，显示其中的最大值和最小值

[root@centos7 ~]# cat test10.sh 
#!/bin/bash
if [ $# -lt 2 ];then
        echo "please input at least two numbers"
        exit 11
fi

declare -i max_num
declare -i min_num
declare -i num=$#
until [ $# = 0 ];do
        if [[ ! "$1" =~ ^[0-9]+$ ]];then 
                echo wrong number $1
                exit
        fi
        if [ $num = $# ];then
                let max_num=$1
                let min_num=$1
        else 
                if [ $1 -gt $max_num ];then
                        let max_num=$1
                elif [ $1 -lt $min_num ];then
                        let min_num=$1
                fi
        fi
        shift
done
echo max=$max_num
echo min=$min_num
[root@centos7 ~]# ./test10.sh 123 132 43 45 89
max=132
min=43