Path: utzoo!censor!geac!torsqnt!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!hplabs!hpda!hpcupt1!hpisod2!decot
From: decot@hpisod2.HP.COM (Dave Decot)
Newsgroups: comp.unix.questions
Subject: Re: Piping into Shell scripts
Message-ID: <10650083@hpisod2.HP.COM>
Date: 4 Mar 90 07:35:49 GMT
References: <1990Feb28.142050.11607@virtech.uucp>
Organization: Hewlett Packard, Cupertino
Lines: 31

> >Is there any way of getting a Shell script (C or Bourne) to recognise
> >whether it is receiving input from a pipe?
> 
> tty(1) will report "not a tty" if it's input is not from a tty. 
> 
> So the following should work:
> 
> 	testdata="`tty`"
> 	if [ "$testdata" = "not a tty" ]; then
> 		echo "we are not running from a terminal.  therefore we must"
> 		echo "be running from a pipe or with stdin redirected from a" 
> 		echo "file of some sort (of course, it also could be closed)"
> 
> 		exit
> 	fi

This is not portable: many systems output different messages for this
same condition, and some systems write the message on the standard
*error* output.  For instance, "Not a typewriter" is a message used
on some systems.

Instead, use:

	if tty -s
	then
	    echo "Running from a terminal"
	else
	    echo "Not running from a terminal"
	fi

Dave Decot