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Re: [BUG] Condition in [[ doesn't fire, with "if" it fires
- X-seq: zsh-users 22515
- From: Peter Stephenson <p.stephenson@xxxxxxxxxxx>
- To: Zsh Users' List <zsh-users@xxxxxxx>
- Subject: Re: [BUG] Condition in [[ doesn't fire, with "if" it fires
- Date: Tue, 28 Feb 2017 11:51:58 +0000
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On Tue, 28 Feb 2017 03:27:36 -0800
Sebastian Gniazdowski <psprint3@xxxxxxxxxxxx> wrote:
> Checked that even:
> [[ "below" = "below" ]] && (( line ++ )) || (( line = stborder ))
> doesn't fire. In the same way. It is the false option that is fired:
Ah, I see what you've done now. I moved this to zsh-users because this
is an interesting point and the above should give folks enough context
to see what I'm talking about; look at zsh-workers for more background.
&& and || don't work the way they do in C, they are simply evaluated
left to right in a symmetric fashion. (Yes, another shell oddity dating
from year zero for Ray to moan about.) Have a look at the grammar tests
for some example.
- Test succeeds.
- So (( line ++ )) run
- line was zero, and with a post increment the value is zero, so status
- (This is the unexpected bit.) On a non-zero status, the shell looks
forward for the next ||, ignoring any &&'s. As I said, there is no
relative priority, just a strict left to right evaluation.
- So it then executes (( line = stborder ))
- I'm guessing stborder is 0, so that's what line is set to.
You *could* fix this up by switching to a pre-increment, but I'd
recommend just going to if/then/else --- it's much more obvious what the
logic actually means.
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