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Re: Stty bug?

From: Bob Proulx
Subject: Re: Stty bug?
Date: Thu, 11 Feb 2010 10:32:32 -0700
User-agent: Mutt/1.5.18 (2008-05-17)

Alan Curry wrote:
> Tom writes:
> > I'm using Ubuntu 9.10 (32-bit).
> > I'm trying to use an ASR-33 Teletype (uppercase only)
> Are you trying to write the best message this mailing list has ever aseen?
> Because so far, it is.

I agree.  It puts my vt100 to shame. :-)

> > As you can see, iuclc is set but no commands work
> I believe -iexten may be the problem. In your tty1 test, was iexten enabled?
> Maybe a getty bug, it should be turning on iexten if it turns on iuclc.

I was able to recreate the original problem.  Reading Alan's response
here I was surprised to see that adding iexten to iuclc did enable the
desired behavior.  This would not have been required on traditional
systems and its combination here isn't obvious to me.  There doesn't
seem to be very much documentation available about iexten.  I am
curious how you deduced that adding it would produce the desired

The documentation says:

  $ info coreutils 'stty invocation'

       Enable non-POSIX special characters.  May be negated.

       Translate uppercase characters to lowercase.  Non-POSIX.  May be

The HP-UX 10.20 man page says the following and makes no mention of

  If IUCLC is set, a received uppercase alphabetic character is
  translated into the corresponding lowercase character.

The SunOS man page says:

    iexten (-iexten)     Enable (disable) special control  characters
                         not currently controlled by icanon, isig,
                         ixon, or ixoff: VEOLZ, VSWTCH, VREPRINT,
                         VDISCARD, VDSUSP, VWERASE, and VLNEXT.

By my reading that doesn't give any hint that iexten is required for
iuclc to function.  And indeed it isn't needed on a pty.  I don't
recall this having been needed on traditional Unix systems to enable
iuclc to function.  It isn't mentioned in the HP-UX documentation.

I still think this is simply a Linux kernel tty driver bug.  I haven't
looked at the code there yet though.


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