From: Mikael Magnusson <mikachu@gmail.com>
To: Kurtis Rader <krader@skepticism.us>
Cc: Thorsten Kampe <thorsten@thorstenkampe.de>,
Zsh Users <zsh-users@zsh.org>
Subject: Re: `[[ -n $VAR ]]` equal to `[[ $VAR ]]`?
Date: Fri, 10 Apr 2015 04:46:58 +0200 [thread overview]
Message-ID: <CAHYJk3Qj6W=VZ26si0VjhsmS1u9go6mVGpXjDSTLk5knKaEtOg@mail.gmail.com> (raw)
In-Reply-To: <CABx2=D93rJDoqGHa=9=nGZZU=9oC_vc-0FHE8ZERV9LmxtqRaA@mail.gmail.com>
On Fri, Apr 10, 2015 at 4:05 AM, Kurtis Rader <krader@skepticism.us> wrote:
> On Thu, Apr 9, 2015 at 7:02 PM, Kurtis Rader <krader@skepticism.us> wrote:
>> On Thu, Apr 9, 2015 at 6:39 PM, Thorsten Kampe <thorsten@thorstenkampe.de>
>> wrote:
>>
>>>
>>> ```
>>> VAR=
>>>
>>> if [[ $VAR ]]
>>> then
>>> printf "something\n"
>>> else
>>> printf "nothing\n"
>>> fi
>>> ```
>>>
>>> Works fine in zsh and bash.
>>>
>>> Same goes for
>>> `[[ $VAR ]] && printf "something\n" || printf "nothing\n"`
>>
>> Okay, I had forgotten that a bare string is equivalent to "-n string" in
>> bash. The zsh documentation makes no mention of this "feature". It probably
>> works for you and not me because of an option that differs between our two
>> environments. Although for the life of me I can't figure out what that
>> option is.
>
> Bart's reply explains why I get a parse error: Mac OS X still has zsh
> v5.0.5 which does not support the bash semantics for a bare string inside
> [[ ]]. Even if you don't need compatibility with pre v5.0.6 zsh releases I
> would discourage that syntax because of its ambiguity.
(please don't top post, it's a lot of work to fix the mail before replying)
If you mean ambiguity because VAR might be the string "-z" for
example, there is no such ambiguity. The syntax of [[ ... ]] is fully
parsed before any substitutions inside are made (I think, but it's at
least true for this purpose). (This is unlike [ ... ] which is not
syntax but a shell builtin that gets passed arguments after they're
substituted, globbed, expanded and etc).
--
Mikael Magnusson
next prev parent reply other threads:[~2015-04-10 2:47 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-10 1:23 Thorsten Kampe
2015-04-10 1:31 ` Kurtis Rader
2015-04-10 1:39 ` Thorsten Kampe
2015-04-10 2:02 ` Kurtis Rader
2015-04-10 2:05 ` Kurtis Rader
2015-04-10 2:46 ` Mikael Magnusson [this message]
2015-04-10 2:59 ` Kurtis Rader
2015-04-10 4:00 ` Mikael Magnusson
2015-04-10 6:06 ` Thorsten Kampe
2015-04-13 16:52 ` Ray Andrews
2015-04-13 17:36 ` Roman Neuhauser
2015-04-13 23:58 ` Ray Andrews
2015-04-14 1:27 ` Bart Schaefer
2015-04-14 15:06 ` Ray Andrews
2015-04-10 3:21 ` Kurtis Rader
2015-04-10 2:01 ` Bart Schaefer
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