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From: dce@mips.UUCP (David Elliott)
Newsgroups: comp.unix.wizards
Subject: Re: Re: /bin/test and stat(2)
Message-ID: <743@quacky.UUCP>
Date: Sat, 3-Oct-87 12:02:57 EDT
Article-I.D.: quacky.743
Posted: Sat Oct  3 12:02:57 1987
Date-Received: Thu, 8-Oct-87 06:28:28 EDT
References: <9479@brl-adm.ARPA> <29056@sun.uucp> <467@ambush.UUCP>
Reply-To: dce@quacky.UUCP (David Elliott)
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 42

In article <467@ambush.UUCP> kimcm@ambush.UUCP (Kim Chr. Madsen) writes:
>In article <29056@sun.uucp> guy%gorodish@Sun.COM (Guy Harris) writes:
>>Don't rely on *this* behavior either - check that a string isn't null before
>>handing it to "/bin/test"!
>
>Just how ? Write a specialized c-program "isnull"....er!
>Otherwise you'll have to use test to test whether it should be passed to
>test.... (-;
>
>Well it's two different uses of test...So I'm just picky I think...

You can use the -a (boolean "and" operator) or -o ("or"). That is

	test " $name" != " " -a -d "$name"

will tell you if "$name" is a directory, whether it is empty
or not. Also,

	test " $name" = " " -o ! -d "$name"

will tell you if "$name" is not a directory.

In both cases, you use a single invokation of the "test" command, so
even old shells without builtin test can work (and if you're worried
about the extra fork/exec's, there's even a way to use "case" and
shell globbing to find out if a file or directory exists with a
single fork).

(Note: I use the construct

	" $name" = " "

because I'm very picky. This is similar to the more common

	$name = ""
	x$name = x

used by many programmers. The former breaks if "$name" is "-d"
or something, and the latter breaks if "$name" contains whitespace.)

-- 
David Elliott		{decvax,ucbvax,ihnp4}!decwrl!mips!dce