From: Oliver Kiddle <okiddle@yahoo.co.uk>
To: Ray Andrews <rayandrews@eastlink.ca>
Cc: zsh-users@zsh.org
Subject: Re: for loop question
Date: Mon, 03 Nov 2014 00:24:11 +0100 [thread overview]
Message-ID: <16789.1414970651@thecus.kiddle.eu> (raw)
In-Reply-To: <5456B3E6.4040907@eastlink.ca>
Ray Andrews wrote:
> > You could with:
> >
> > for ((i=1; (z[$([ -n "$TLC[i]" ])0]),$? == 0; i++))
> > print -ru2 -- $TLC[i]
> >
> > (not that you would want to).
> No. That is pure sadism ;-) ;-)
>
> But it does show that 'for ((' CAN stop and digest ' [ -n "$TLC[i]" ]
> ' if it wants too,
> it just has to make it obscenely difficult. Why can't the truth test of
> a command just be taken
> as 'arithmetic' plain and simple?
Inside of (( ... )) is arithmetic context. So different syntax is valid
there. [ is just a command. Look at the error message you get if you put
it there:
% for ((; [ -f foo ] ; )) echo true
zsh: bad output format specification
Zsh sees the square brackets and in arithmetic context, square brackets
are used for selecting an output format, specifically a number base. For
example:
% echo $(( [#2] 37 ))
2#100101
There's also a command named true which just returns true. So what do
you think the following might do:
% for ((; true ;)) echo true!
This actually looks for the variable $true and interprets it as a
number.
As you can see, the syntaxes conflict. While we could add a simple way
to escape back into normal syntax from arithmetic syntax, it'd be no
nicer than the existing alternatives.
Oliver
next prev parent reply other threads:[~2014-11-02 23:31 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-02 20:47 Ray Andrews
2014-11-02 21:00 ` Bart Schaefer
[not found] ` <CAH+w=7aWS0xyS4CXRJBphDjesfUFQOsyJRMaG3RZRxmuj7xkOg__20885.3257158355$1414962125$gmane$org@mail.gmail.com>
2014-11-02 21:37 ` Stephane Chazelas
2014-11-02 22:44 ` Ray Andrews
2014-11-02 22:57 ` Bart Schaefer
2014-11-02 23:24 ` Oliver Kiddle [this message]
2014-11-03 0:07 ` Ray Andrews
2014-11-03 1:53 ` Mikael Magnusson
2014-11-03 2:22 ` Ray Andrews
2014-11-03 9:22 ` Mikael Magnusson
2014-11-03 17:26 ` Ray Andrews
2014-11-04 1:56 ` Han Pingtian
2014-11-04 2:29 ` Han Pingtian
2014-11-04 2:43 ` Bart Schaefer
2014-11-04 4:51 ` Han Pingtian
2014-11-04 6:37 ` Ray Andrews
2014-11-04 7:13 ` Bart Schaefer
2014-11-04 18:00 ` Ray Andrews
[not found] ` <141103184338.ZM32221__48957.5251042426$1415069142$gmane$org@torch.brasslantern.com>
2014-11-04 7:08 ` Stephane Chazelas
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