sh-4.1# nc -w 5 baidu.com 80 && echo ok
ok
sh-4.1# nc -w 5 baidu.com 81
sh-4.1# echo $?
1
sh-4.1# nc -w 5 baidu.com 80
sh-4.1# echo $? #返回上面命
0
telnet 查看端口是否开启：
sh-4.1# telnet baidu.com 84
Trying 111.13.101.208...
telnet: connect to address 111.13.101.208: Connection timed out
百度开了80，而并没开84所以，连84端口失败
sh-4.1# telnet baidu.com 80
Trying 123.125.114.144...
Connected to baidu.com.
Escape character is '^]'.
网名：bass 分享技术 突破难点 创新思维
