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From: dce@mips.UUCP
Newsgroups: comp.bugs.4bsd
Subject: Re: Bug/Feature in `test' - (nf)
Message-ID: <256@quacky.mips.UUCP>
Date: Fri, 3-Apr-87 09:53:57 EST
Article-I.D.: quacky.256
Posted: Fri Apr  3 09:53:57 1987
Date-Received: Sun, 5-Apr-87 05:38:35 EST
References: <6200001@iaoobelix.UUCP>
Reply-To: dce@quacky.UUCP (David Elliott)
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 51

In article <6200001@iaoobelix.UUCP> wagner@iaoobelix.UUCP writes:
>The file `try' contains the following:
>
>	#! /bin/sh
>	if [ "$1" = "-d" ] 
>	then
>	    echo ok
>	fi
>
>The I typed in:
>
>	% try 8
>	bad
>	% try -d

This answer may not be the one you are fishing for, but I think it is
useful nonetheless.

When you say "try -d", the test line gets interpreted as

	[ "-d" = "-d" ]

which is syntactically incorrect given the definition of test, which says
that a -d is followed by a name which is checked to see if it is a
directory. It doesn't specifically say that '=' takes precedence over '-d',
so you can never assume that it does (or that '-d' takes precedence).

You have to be completely clear (I want to say unambiguous, but won't).

My own habit is to always say

	[ " value" op " value" ]

This has three advantages:

	1. It is syntactically clear.
	2. It forces you to put quotes around the values, which avoids
	   problems with variables containing spaces/tabs, and makes the
	   values stand out.
	3. It is aesthetically pleasing (as opposed to the more common

		[ xvalue op xvalue ]

	   which breaks when spaces/tabs are used)

As an alternative, 'case' works quite well for string comparisons, and
for number equality if you know what the numbers look like (i.e., you
can check for $# being equal to a specific value, since $# will be
expanded with no extra spaces or tabs or leading 0s).
-- 
David Elliott		{decvax,ucbvax,ihnp4}!decwrl!mips!dce