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Check the intended interpreter and run a syntax check first. Enable xtrace only around the suspect section because it prints expanded values; redirect diagnostics securely and mask credentials. Reproduce with controlled input, inspect each command status, and use ShellCheck to catch common quoting and portability issues.

Unlike TCP, UDP does not establish a transport connection before sending a datagram. A missing response can mean filtering, packet loss, an invalid request, or an application that does not reply. Use a valid protocol-level health check and capture at sender and receiver when diagnosing the path.

TCP connection establishment and retransmission make a port-connectivity test meaningful, but application message boundaries still need framing. UDP has no handshake, so silence may mean a dropped packet, invalid request, or a service that does not answer probes. Test using a valid protocol request and inspect both ends when possible.

Use the system resolver path, for example getent hosts, and compare with a direct DNS query. If a correct address resolves but the connection fails, investigate route, listener, firewall, or protocol behavior. Run diagnostics inside the same container or namespace as the application because resolver configuration may differ.