例如需要扫描某个机器上21-30哪些端口是开放的： $nc-n127.0.0.1-z1230-1234-v nc:connectto127.0.0.1port1230(tcp)failed:Connectionrefused nc:connectto127.0.0.1port1231(tcp)failed:Connectionrefused nc:connectto127.0.0.1port1232(tcp)failed:Conn