====== 使用 nc 读写 TCP/UDP 连接 ======
https://www.ifmicro.com/%E8%AE%B0%E5%BD%95/2017/12/12/netcat-usage/

======linux下详解shell中>/dev/null 2>&1======
https://www.cnblogs.com/ultranms/p/9353157.html