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From: aj@zyx.UUCP (Arndt Jonasson)
Newsgroups: comp.unix.questions
Subject: What is the name of /dev/tty?
Message-ID: <1418@zyx.UUCP>
Date: Mon, 12-Oct-87 12:54:26 EDT
Article-I.D.: zyx.1418
Posted: Mon Oct 12 12:54:26 1987
Date-Received: Sun, 18-Oct-87 08:48:00 EDT
Reply-To: aj@zyx.SE (Arndt Jonasson)
Organization: ZYX Sweden AB, Stockholm
Lines: 26


Is there any way in Unix (either BSD or SYS5) to obtain the true name
of the process's controlling terminal?

In other words, if my program opens /dev/tty, how can it find out which
real terminal this corresponds to? The real name may be something like
/dev/ttyp2.

Examples (imagine 'prog' being run on /dev/ttyp2):

prog >foo		Here isatty(3) says that stdout is not a tty, so
			this case is easy.

prog			Here /dev/tty and stdout are 'the same'.

prog >/dev/ttyp6	Here they are not.

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.
-- 
Arndt Jonasson, ZYX Sweden AB, Styrmansgatan 6, 114 54 Stockholm, Sweden
email address:	 <backbone>!mcvax!enea!!zyx!aj	=	aj@zyx.SE