Path: utzoo!attcan!uunet!mcvax!ukc!warwick!alfie
From: alfie@warwick.UUCP (Nick Holloway)
Newsgroups: comp.unix.questions
Subject: Re: correct isatty usage
Keywords: isatty(3), tty(1)
Message-ID: <1377@ubu.warwick.UUCP>
Date: 28 Feb 89 10:05:22 GMT
References: <18432@adm.BRL.MIL> <1161@tikal.Teltone.COM>
Sender: news@warwick.UUCP
Reply-To: alfie@uk.ac.warwick.cs (Nick Holloway)
Organization: Computer Science, Warwick University, UK
Lines: 45

In article <1161@tikal.Teltone.COM> dave@tikal.UUCP (David Karr) writes:
> In article <18432@adm.BRL.MIL> Pabbisetty.henr@xerox.com (Nagesh Pabbisetty) writes:
> >> [Doing isatty(FILE*) instead of isatty(int)]
> >
> > [Correct solution of isatty(fileno(FILE*))]
> 
> Now my question is, how would you do this in a script?  Either C or Bourne.

The method I use is tty(1). This will print out the name of the terminal
attached to stdin. This can be used more generally by using the -s flag (No
report just, return the status) and redirecting the input. 
This script is an example of this (call it demo):
	#!/bin/sh
	if tty -s <&0			# redirect from stdin
	then echo "stdin:  from terminal"
	else echo "stdin:  not from terminal"
	fi
	if tty -s <&1			# redirect from stdout
	then echo "stdout: from terminal"
	else echo "stdout: not from terminal"
	fi
	if tty -s <&2			# redirect from stderr
	then echo "stderr: from terminal"
	else echo "stderr: not from terminal"
	fi

Try running as:
	$ demo
	$ demo | cat
	$ demo 2>/dev/null
	$ demo 2>&1 | cat
	$ demo </dev/null 2>&1 | cat

> In C shell, I have this code, but it doesn't appear to work.
> 	[C-Shell script to try and find out whether connected to terminal]

I'm afraid I don't speak c-shell, so I can't comment on your script - although
if you are only interested in whether stdin is connected to terminal you can
use "tty -s" as above. When it comes to checking other streams - I don't know
enough about C-shell redirection (other than it is not as flexible as sh).
--
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