Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!cs.utexas.edu!uunet!mcsun!hp4nl!star.cs.vu.nl!maart
From: maart@cs.vu.nl (Maarten Litmaath)
Newsgroups: comp.unix.questions
Subject: Re: How do I ask "if NOT" in shell?
Message-ID: <3787@solo6.cs.vu.nl>
Date: 23 Oct 89 18:38:43 GMT
References: <28381@shemp.CS.UCLA.EDU>
Organization: V.U. Informatica, Amsterdam, the Netherlands
Lines: 31

kirkaas@oahu.cs.ucla.edu (paul kirkaas) writes:
\How can one say "if not" in a shellscript; that is, execute the body of
\the "then" only if the argument of "if" returns a non-zero exit status?

Unfortunately there doesn't seem to be a clean way to do this.
The obvious work-around:

	if command
	then
		:
	else
		command
	fi

A cleaner approach:

	if not command
	then
		command
	fi

...where `not' is defined as the following shell function/script:

	${1+"$@"}
	test $? != 0

SunOS 4.0.3c /bin/sh doesn't like a function to be named `!', a shell
script would be OK though.
-- 
A symbolic link is a POINTER to a file, | Maarten Litmaath @ VU Amsterdam:
 a hard link is the file system's GOTO. | maart@cs.vu.nl, mcsun!botter!maart