Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!gatech!uflorida!haven!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.unix.questions
Subject: sh if-then-else (was Re: How to tell if you're in a pipe...)
Keywords: pipe tty(1) sh(1) isatty(4)
Message-ID: <18353@mimsy.UUCP>
Date: 1 Jul 89 20:31:46 GMT
References: <1798@lgnp1.LS.COM>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 25

In article <1798@lgnp1.LS.COM> rbarrell@lgnp1.LS.COM (Robert Barrell) writes:
>     if [ `tty -s;echo $?` = 0 ]

This is rather the hard way around: a simple

	if tty -s

will suffice.  The result of

	if list; then true-branch; else false-branch; fi

is `true' if the exit status (here, `$?') of the command-list `list'
is zero, and false otherwise, so that the `if' runs the true-branch
if `tty -s' exits 0 and the false-branch if `tty -s' exits nonzero (1).

To get this effect in the C shell, one must write

	if { tty -s } then

(`if ({ list }) then' is also accepted).  Watch the spacing; the
words `if' and `then' must not be run into their parentheses or
braces.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris