1、端口未打开$ telnet 101.199.97.65 62715 Trying 101.199.97.65... telnet: connect to address 101.199.97.65: Connection refused
2、端口已打开$ telnet 101.199.97.65 6271猱蝰逾鸾5 Trying 101.199.97.65... Connected to 101.199.97.65. Escape character is '^]'.此时命令未退出。根据提示Escape character is '^]'.可知退出字符为'^]'（CTRL+]）。此时输入其它字符不能使其退出，CTRL+C都不行。本文所有工具都可以在《Linux就该这么学》这本书中找到，详细的讲解！输入CTRL+]后会自动执行，进入命令模式：^] telnet>此时再运行quit才会真正退出。telnet> quit Connection closed.其中，Escape character可以自定义，使用参数-e：$ telnet -e p 101.199.97.65 62715 #使用p字符 Telnet escape character is 'p'. Trying 101.199.97.65... Connected to 101.199.97.65. Escape character is 'p'. p telnet> quit Connection closed.即便如此，退出telnet还是麻烦。那么，更进一步，如果出现在脚本中应该如何（优雅地）退出telnet呢？
3、输出结果后立即退出$ echo "" | telnet 101.199.97.65 62715 Trying 101.199.97.65... Connected to 101.199.97.65. Escape character is '^]'. Connection closed by foreign host. #已成功连通端口并自动退出$ echo "" | telnet 101.199.97.65 62715 Trying 101.199.97.65... telnet: connect to address 101.199.97.65: Connection refused #端口未开放
4、输出结果后延迟退出sleep 2使得telnet输出结果后，停留2秒后退出命令模式。$ sleep 2 | telnet 101.199.97.65 62715 Trying 101.199.97.65... Connected to 101.199.97.65. Escape character is '^]'. Connection closed by foreign host.使用这种方式可以将标准输出和标准错误重定向到文件中，通过分析文件的内容来判断端口打开状态。
