[root@localhost ~]# cat telnetscript.sh
#!/bin/bash
#检查是否在root用户下执行此脚本(0代表root用户的权限)
if [ $(id -u) != "0" ];then
        echo "请在root用户下运行脚本"
        exit 1
fi
#定义输出目录
DIR="/var/log/"
TIME="$(date +%Y-%m-%d,%X)"
IP=ip地址或域名
PORT=端口号
#下面需要先安装nmap工具
checkPort(){
        #检查端口开通情况，输出端口的开通信息(443/tcp open  https)
        portState=$(nmap -P0 -sS -p${PORT} ${IP} | awk ‘/STATE/{getline line;print line}‘ | awk ‘{print $2}‘)
        if [ X"${portState}" == X"open" ];then
                echo "${IP} ${PORT} is open" >> ${DIR}telnetstatus.log
                echo "${TIME}" >> ${DIR}telnetstatus.log
        else
                echo "${IP} ${PORT} is failure" >> ${DIR}telnetstatus.log
                echo "${TIME}" >> ${DIR}telnetstatus.log
        fi
}
while true;
do
        checkPort
sleep 3
done

[root@localhost ~]# ./telnetscript.sh &
[1] 30257

[root@localhost ~]# less /var/log/telnetstatus.log
[root@localhost ~]# wc -l /var/log/telnetstatus.log

[root@localhost ~]# fg
./telnetscript.sh
[root@localhost ~]# jobs