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From: Bart Schaefer <schaefer@brasslantern.com>
To: Zsh hackers list <zsh-workers@zsh.org>
Subject: Square brackets in command position
Date: Wed, 9 Jun 2021 17:14:55 -0700	[thread overview]
Message-ID: <CAH+w=7Yj73_DjDmNVPgkXqrTm=3j6Hd5640eiOuhxi7dqiVG3Q@mail.gmail.com> (raw)
In-Reply-To: <20210605170531.af3rj3iurjvvcmdw@chazelas.org>

On Sat, Jun 5, 2021 at 10:05 AM Stephane Chazelas <stephane@chazelas.org> wrote:
>
> 2021-06-04 17:20:29 -0700, Bart Schaefer:
> [...]
> > > array[1 + 1]=4
> > >
> > > That is pretty annoying.
> >
> > That's just shell whitespace rules, though.
>
> Note that all other shells that support a[1]=value (ksh, pdksh,
> bash) do it.

Chip will probably correct me, but from some experiments with bash it
appears that (with the exception of '[' all alone, to invoke "test")
an (unquoted) '[' in a word in command position always begins an
expression that must be bounded by a closing (unquoted) ']' (even if
that means continuing to the PS2 prompt).  Thus for example
  $ a[ 1 + 1 ]b
globs to a file named "a b" in the current directory and does a path
search to run that as a command.  Note that
 $ [a ]b
globs to "ab" or " b" (leading space there if that's hard to see),
it's not what's to the left of '[' that triggers this.

Thus it's not just assignments that have command-position magic,
character classes can have embedded (unquoted) spaces there as well.
This breaks if you are looking for a file named e.g. "a+=" because
']=' turns the whole thing into an array element assignment.

> There is variation in behaviour between shells if the first word
> starts with name[ and either a matching ] or matching ] followed
> by = is not found, and how that matching is done or what kind of
> quoting are supported inside the [...].

That doesn't give us any good ideas on where to start.  Of course
zsh's parsing hash keys using the same quoting rules as arithmetic was
a quick way to slurp hash[string] through the existing array[math]
parser at the time, and in retrospect probably should have been given
its own rules.

> In zsh, that would be even less problematic as (at least when
> not in sh emulation), zsh complains about unmatched [s or ]s

As mentioned before, that's the BAD_PATTERN setopt, which can be
turned off independent of emulation, so it might be a stretch to say
we wouldn't be breaking anything.


  reply	other threads:[~2021-06-10  0:15 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-16 21:10 regexp-replace and ^, word boundary or look-behind operators Stephane Chazelas
2019-12-16 21:27 ` Stephane Chazelas
2019-12-17  7:38   ` Stephane Chazelas
2019-12-17 11:11     ` [PATCH] " Stephane Chazelas
2019-12-18  0:22       ` Daniel Shahaf
2019-12-18  8:31         ` Stephane Chazelas
2020-01-01 14:03         ` [PATCH v2] " Stephane Chazelas
2021-04-30  6:11           ` Stephane Chazelas
2021-04-30 23:13             ` Bart Schaefer
2021-05-05 11:45               ` [PATCH v3] regexp-replace and ^, word boundary or look-behind operators (and more) Stephane Chazelas
2021-05-31  0:58                 ` Lawrence Velázquez
2021-05-31 18:18                 ` Bart Schaefer
2021-05-31 21:37                   ` [PATCH] (?) typeset array[position=index]=value Bart Schaefer
2021-06-01  5:32                     ` Stephane Chazelas
2021-06-01 16:05                       ` Bart Schaefer
2021-06-02  2:51                         ` [PATCH] (take two?) typeset array[position=index]=value / unset hash[$stuff] Bart Schaefer
2021-06-02 10:06                           ` Stephane Chazelas
2021-06-02 14:52                             ` Bart Schaefer
2021-06-02 16:02                               ` Stephane Chazelas
2021-06-02  9:11                         ` [PATCH] (?) typeset array[position=index]=value Stephane Chazelas
2021-06-02 13:34                           ` Daniel Shahaf
2021-06-02 14:20                             ` Stephane Chazelas
2021-06-02 15:59                               ` Bart Schaefer
2021-06-03  2:04                                 ` [PATCH (not final)] (take three?) unset "array[$anything]" Bart Schaefer
2021-06-03  2:42                                   ` Bart Schaefer
2021-06-03  6:12                                     ` Bart Schaefer
2021-06-03  8:54                                       ` Peter Stephenson
2021-06-03 13:13                                         ` Stephane Chazelas
2021-06-03 14:41                                           ` Peter Stephenson
2021-06-04 19:25                                             ` Bart Schaefer
2021-06-05 18:18                                               ` Peter Stephenson
2021-06-09 23:31                                                 ` Bart Schaefer
2021-06-13 16:51                                                   ` Peter Stephenson
2021-06-13 18:04                                                     ` Bart Schaefer
2021-06-13 19:48                                                       ` Peter Stephenson
2021-06-13 21:44                                                         ` Bart Schaefer
2021-06-14  7:19                                                           ` Stephane Chazelas
2021-06-03 18:12                                           ` Bart Schaefer
2021-06-04  8:02                                             ` Stephane Chazelas
2021-06-04 18:36                                               ` Bart Schaefer
2021-06-04 20:21                                                 ` Stephane Chazelas
2021-06-05  0:20                                                   ` Bart Schaefer
2021-06-05 17:05                                                     ` Stephane Chazelas
2021-06-10  0:14                                                       ` Bart Schaefer [this message]
2021-06-03  6:05                                   ` Stephane Chazelas
2021-06-03  6:43                                     ` Bart Schaefer
2021-06-03  7:31                                       ` Stephane Chazelas
2021-06-10  0:21                         ` [PATCH] (?) typeset array[position=index]=value Bart Schaefer
2021-06-05  4:29                     ` Mikael Magnusson
2021-06-05  5:49                       ` Bart Schaefer
2021-06-05 11:06                         ` Mikael Magnusson
2021-06-05 16:22                           ` Bart Schaefer
2021-06-18 10:53                         ` Mikael Magnusson
2024-03-08 15:30                 ` [PATCH v3] regexp-replace and ^, word boundary or look-behind operators (and more) Stephane Chazelas
2024-03-09  8:41                   ` [PATCH v5] " Stephane Chazelas
2024-03-09  9:21                     ` MBEGIN when =~ finds bytes inside characters (Was: [PATCH v5] regexp-replace and ^, word boundary or look-behind operators (and more).) Stephane Chazelas
2024-03-09 13:03                   ` [PATCH v3] regexp-replace and ^, word boundary or look-behind operators (and more) Stephane Chazelas
2024-03-10 19:52                     ` [PATCH v6] " Stephane Chazelas

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