while TRUE; do { echo -e 'HTTP/1.1 200 OK\r\n'; cat /path/to/thing; } | nc -l 8000; done

From: https://krypted.com/

Neither echo -e nor nc are POSIX. I don't think there is a strictly POSIX one-liner.

`echo -e` should be easily replaceable with `printf` but nc remains to be a problem.

Is inetd "Posix"? It has command line switches to not fork, and to specify the config file. Maybe it takes a config file of "-" to mean stdin.

I doubt it. At least I can't find it anywere here:

https://pubs.opengroup.org/onlinepubs/9699919799/utilities/c...

You are right, but it was the closest I could find.

printf(1) is POSIX and is a superset of echo.