在 bash 中监听返回的 UDP 数据包
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listen for returning UDP packets in bash
提问by Martin
I played around with bash(4.0.33) network support for learning purposes and tried to create a port scanner in bash. For TCP I opened a TCP/IP socket with
为了学习目的，我尝试了 bash(4.0.33) 网络支持，并尝试在 bash 中创建端口扫描器。对于 TCP，我打开了一个 TCP/IP 套接字
exec 3<>/dev/tcp/192.0.2.1/80
exec 3<>/dev/tcp/192.0.2.1/80
and appropriate action was taken if the connection was refused or connectsystem call timed out. However, with UDP I'm easily able to send a packet with
如果连接被拒绝或连接系统调用超时，则采取适当的措施。但是，使用 UDP，我可以轻松发送数据包
echo > /dev/udp/192.0.2.1/53
echo > /dev/udp/192.0.2.1/53
but how to read returning packets from correct socket? I mean UDP datagram sent to 192.0.2.1 has source port from ephemeral port range and thus I do not know which socket in /dev/udp/192.0.2.1/directory should I read. Or isn't this doable without external utilities like tcpdump?
但是如何从正确的套接字读取返回的数据包？我的意思是发送到 192.0.2.1 的 UDP 数据报具有来自临时端口范围的源端口，因此我不知道/dev/udp/192.0.2.1/应该读取目录中的哪个套接字。或者，如果没有像tcpdump这样的外部实用程序，这是否可行？
回答by that other guy
Bash's UDP support isn't great, and is compiled out on many distros (Debian/Ubuntu and derivatives especially). The recommended tool is netcat:
Bash 的 UDP 支持不是很好，并且在许多发行版（尤其是 Debian/Ubuntu 和衍生版）上编译出来。推荐的工具是netcat：
nc -u 192.0.2.1 53
Note: Use coproc or named pipes to read and write from the same netcat process. Don't send a packet first and try to catch the reply netcat.
注意：使用 coproc 或命名管道从同一个 netcat 进程读取和写入。不要先发送数据包并尝试捕获回复 netcat。
Bash is really the wrong language for this though. Consider using Python, which handles both UDP and binary data way better, with just a couple of more lines of code.
尽管如此，Bash 确实是错误的语言。考虑使用 Python，它可以更好地处理 UDP 和二进制数据，只需多几行代码。
