Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!bbn!rochester!PT.CS.CMU.EDU!sei!sei.cmu.edu!pdb
From: pdb@sei.cmu.edu (Patrick Barron)
Newsgroups: comp.unix.questions
Subject: Re: What is the name of /dev/tty?
Message-ID: <2903@aw.sei.cmu.edu>
Date: Sun, 18-Oct-87 01:53:23 EDT
Article-I.D.: aw.2903
Posted: Sun Oct 18 01:53:23 1987
Date-Received: Sun, 18-Oct-87 22:56:24 EDT
References: <1418@zyx.UUCP>
Sender: netnews@sei.cmu.edu
Reply-To: pdb@sei.cmu.edu (Pat Barron)
Organization: Carnegie-Mellon University, SEI, Pgh, Pa
Lines: 23

In article <1418@zyx.UUCP> aj@zyx.SE (Arndt Jonasson) writes:
>
>Is there any way in Unix (either BSD or SYS5) to obtain the true name
>of the process's controlling terminal?

On 4BSD, you can find out the terminal connected to /dev/tty by digging
it out of your process's u area.  If you don't have read access to /dev/kmem,
your process can fork off a child temporarily, and use ptrace(2) to get at
the info.  This will yield the major and minor device numbers of the
controlling tty (or zero, if your process isn't attached to a terminal).
You could also look for your own entry in /etc/utmp the way "who am i"
does.

>The reason why it would be interesting to know this is that I want my
>program to know whether its standard output and its controlling terminal
>are the same, in the sense that output to the two streams will mix on
>the same window/screen. Error messages will use /dev/tty only if it is
>not the same as stdout, to avoid mixing of output from different write
>operations on the screen.

Why not just use stderr for error messages instead?

--Pat.