Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!cs.utexas.edu!uunet!auspex!hitz
From: hitz@auspex.auspex.com (Dave Hitz)
Newsgroups: comp.unix.questions
Subject: Re: How do I ask "if NOT" in shell?
Message-ID: <2558@auspex.auspex.com>
Date: 23 Oct 89 22:21:55 GMT
References: <28381@shemp.CS.UCLA.EDU>
Reply-To: hitz@auspex.auspex.com (Dave Hitz)
Organization: Auspex Systems, Santa Clara
Lines: 34

In article <28381@shemp.CS.UCLA.EDU> kirkaas@oahu.UUCP (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?
>
>I would like something like:
>
>if ! TESTCOMMAND
>then
>	BODY
>fi

I often define the following in my shell scripts.

	    NOT() {
		if ${1+"$@"}
		then return 1;
		else return 0;
		fi
	    }

Unfortunately, not all shells support functions yet, but for those that
do this works fine.  You can use this just like you requested:

	    if NOT grep foobar /etc/passwd >&-
	    then
		    BODY
	    fi

Picky people may observe that the arguments to NOT get expanded by
the shell twice, but I've never been caught by this.

-- 
Dave Hitz					home: 408-739-7116
UUCP: {uunet,mips,sun,bridge2}!auspex!hitz 	work: 408-970-8970