sh if-then-else (was Re: How to tell if you're in a pipe...)

[Chris Torek]

In article <1798 at lgnp1.LS.COM> rbarrell at 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 at mimsy.umd.edu	Path:	uunet!mimsy!chris