I hope you will agree that Solaris 10 counts as a modern Unix variant. I wanted to use the serial system console on ttya. I connected a serial cable to second Solaris 10 system. On that 2nd system, I opened a terminal window and in that window in used tip to connect. That all works fine. But when I vary the window size on the 2nd system, the first system does not seem to be informed. And no fair telling me that I manually type "stty cols 100" (or whatever) after I change my window size.

The Solaris driver used to control ttya (and ttyb) is indeed a real terminal. The other kind of terminal is a pseudo terminal. In the case of a real terminal, where a real tty driver is truely controlling a real serial port, this isn't going to work. It's true that the old printing teletypes are almost completely gone. Ditto those "ascii terminals" too. But the serial port is still alive and well. We either use another unix system as above or a laptop running putty on XP or something like that to connect to a serial port.

This isn't to say that I dislike your solution. I think your solution is as good as it gets. I am arguing that the search for an even more generic solution is futile and that there no help to be had from Posix.

And also note that jlliagre replaced awk with a grep/sed combo. Solutions involving awk are very dangerous on Solaris. Sun absolutely refuses to retire the antique version of awk so you must either use nawk or fiddle with the path on Solaris.