DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:subject:to:references:from:message-id:date
	:mime-version:in-reply-to:content-type
	:content-transfer-encoding; q=dns; s=default; b=LgsmtqVG1aUI2C6u
	nSSRslv89yJRDSQjOSi4YvwRB0nN09RjK//STPbXHMXd0bhwNBmMz9tRKMTtwzLi
	/Mafj9K4gvarKyQN4ZqBiA0dM0b9Orgba9T/ntc5Sbpx3rHLF8fmvyIXpmjGEMSR
	CB2Bnc1fgVEhSuKkR3a7OuMSViA=
Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm
Sender: cygwin-owner@cygwin.com
Mail-Followup-To: cygwin@cygwin.com
Subject: Re: bash string-operator problem
To: cygwin@cygwin.com
References: <d846545ebaa5469d90f01f84e4f48c3d@vsrv060ex01.ssd.fsi.com> <CAD8GWsvqXdG-2YvmVAqW=jkZ_ejHGOj=LCemjoqkF08Vy7i=Fw@mail.gmail.com> <608a0fe0-a1eb-6c13-8a6e-0074dcbc166c@mail.com> <CAD8GWsvUBHrbTNxE1RA1gtUhXCD3tD6BgUuPBX_DWJDwHOafDg@mail.gmail.com>
From: Eric Blake <eblake@redhat.com>
Message-ID: <7fbf3ef0-35fc-7c00-8f8f-ce90cb281edd@redhat.com>
Date: Thu, 21 Feb 2019 14:24:45 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0
MIME-Version: 1.0
In-Reply-To: <CAD8GWsvUBHrbTNxE1RA1gtUhXCD3tD6BgUuPBX_DWJDwHOafDg@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit

On 2/21/19 2:17 PM, Lee wrote:

>>
>> One equal sign ('=') should be used instead of two equal signs ('==').
> 
> The man page for test says you're correct, but just out of curiosity
> -- why do two equal signs work?

Use of [ ... == ... ] is a bash extension. It works in bash, but is not
portable to other /bin/sh (notoriously == fails in dash, and is not
required by POSIX).

Oddly enough, POSIX is considering standardizing a common subset of [[;
in that case, [[ ... = ... ]] is non-portable, and the proposal only
documents [[ ... == ... ]] as being valid.  For more than you ever
wanted to know, read http://austingroupbugs.net/view.php?id=375

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple