Why zsh chose to be non-compliant in pattern matching

Why zsh chose to be non-compliant in pattern matching

[Cuong Manh Le]

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POSIX documentation for pattern matching (
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_13_01)
said that any quoted characters in pattern will be match literally.

AFAICT, `["!"a]` will match `!` or `a`, most of shell behave like that
except zsh (and also ksh):

case a in ["!"a]) echo 1;; esac


print nothing. While:

case b in ["!"a]) echo 1;; esac


print 1. zsh treats `["!"a]` the same as `[!a]`.

Is there any reason for this behavior?

PS: The full question can be seen here
http://unix.stackexchange.com/q/265431/38906

Thanks.

Re: Why zsh chose to be non-compliant in pattern matching

[Bart Schaefer]

This has been changed for the forthcoming 5.3 release (no date yet).
See thread starting here:
http://www.zsh.org/mla/workers//2016/msg00202.html

Re: Why zsh chose to be non-compliant in pattern matching

[Cuong Manh Le]

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Hi,

The super user in U&L site post his opinion at
http://unix.stackexchange.com/a/266394/38906

He said that the pattern matching spec is unspecified for quoted characters
inside bracket expression. What is your opinion?

Thanks.

On Fri, Feb 26, 2016 at 3:43 PM, Bart Schaefer <schaefer@brasslantern.com>
wrote:

> This has been changed for the forthcoming 5.3 release (no date yet).
> See thread starting here:
> http://www.zsh.org/mla/workers//2016/msg00202.html
>

Re: Why zsh chose to be non-compliant in pattern matching

[Peter Stephenson]

On Mon, 29 Feb 2016 17:00:28 +0700
Cuong Manh Le <cuong.manhle.vn@gmail.com> wrote:
> The super user in U&L site post his opinion at
> http://unix.stackexchange.com/a/266394/38906
> 
> He said that the pattern matching spec is unspecified for quoted characters
> inside bracket expression. What is your opinion?

He's talking about the standard, which indeed doesn't say anything about
the subject.

[
    If an open bracket introduces a bracket expression as in XBD RE
    Bracket Expression, except that the <exclamation-mark> character (
    '!' ) shall replace the <circumflex> character ( '^' ) in its role
    in a non-matching list in the regular expression notation, it shall
    introduce a pattern bracket expression. A bracket expression
    starting with an unquoted <circumflex> character produces
    unspecified results. Otherwise, '[' shall match the character
    itself.

There's a reference there to regular expressions, for which only
backslash quoting is valid, as far as I'm aware.  Zsh has supported
that for quite a while.

I think it's more a question of current practice.  It's probably
widespread enough now to be standardisable.

pws

Re: Why zsh chose to be non-compliant in pattern matching

[Martijn Dekker]

Peter Stephenson schreef op 29-02-16 om 11:27:
> On Mon, 29 Feb 2016 17:00:28 +0700
> Cuong Manh Le <cuong.manhle.vn@gmail.com> wrote:
>> The super user in U&L site post his opinion at
>> http://unix.stackexchange.com/a/266394/38906
>>
>> He said that the pattern matching spec is unspecified for quoted characters
>> inside bracket expression. What is your opinion?
> 
> He's talking about the standard, which indeed doesn't say anything about
> the subject.

In my view, the standard is quite clear:

"If any character (ordinary, shell special, or pattern special) is
quoted, that pattern shall match the character itself."

That sentence applies to pattern matching notation as a whole. Bracket
expressions are a part of pattern matching notation. There is no
language anywhere in the standard that excludes bracket expressions from
the sentence quoted.

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_13

Thanks,

- M.