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Date: Sat, 9 Oct 2010 18:17:01 -0400
From: Phil Pennock <zsh-workers+phil.pennock@spodhuis.org>
To: Michael Hwang <michael.a.hwang@gmail.com>
Cc: Mikael Magnusson <mikachu@gmail.com>, zsh workers <zsh-workers@zsh.org>,
	brandon@ifup.org
Subject: Re: [[ 0 =~ 1 || 1 = 0 ]] returns true
Message-ID: <20101009221700.GA60765@redoubt.spodhuis.org>
Mail-Followup-To: Michael Hwang <michael.a.hwang@gmail.com>,
	Mikael Magnusson <mikachu@gmail.com>,
	zsh workers <zsh-workers@zsh.org>, brandon@ifup.org
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On 2010-10-09 at 16:06 -0400, Michael Hwang wrote:
> % set -x
> % [[ 0 =~ 1 || 1 = 0 ]]
> +zsh:2> [[ 0 -regex-match 1 || ! 1 == 0 ]]
> % [[ 0 =~ 1 || 1 == 1 || 1 = 0 ]]
> +zsh:3> [[ 0 -regex-match 1 || ! 1 == 1 ]]
> % [[ 0 =~ 1 || 1 == 1 || 1 = 1 || 1 = 1 || 1 = 1 ]]
> +zsh:4> [[ 0 -regex-match 1 || ! 1 == 1 ]]
> 
> It appears that zsh thinks it needs to invert the second conditional
> expression. Also, zsh seems to drop more than two conditional
> expressions.

The dropping is short-circuiting, the same as in all shell evaluation of
&& and ||.  The shell stops once it knows enough to know the answer.  So
false to the left of && will stop, and true to the left of || will stop.

% [[ 1 == 1 && 3 == 2 && 4 == 4 && sb == sb ]]
+zsh:12> [[ 1 == 1 && 3 == 2 ]]
% [[ 1 == 1 && 3 != 2 && 4 == 4 && sb == sb ]]
+zsh:13> [[ 1 == 1 && 3 != 2 && 4 == 4 && sb == sb ]]

So the issue appears to just be what the OP wrote, that =~ is messing up
&&/|| by inserting a sense inversion.

% [[ 1 =~ 0 || 1 == 1 ]]
+zsh:18> [[ 1 -regex-match 0 || ! 1 == 1 ]]
% [[ 1 -regex-match 0 || 1 == 1 ]]
+zsh:19> [[ 1 -regex-match 0 || 1 == 1 ]]

So it's related to use of =~ rather than -regex-match.  It's independent
of whether or not zsh/pcre is loaded.  So this is probably a bug which I
introduced when I wrote the =~ syntax support.  Looking now.

-Phil