From: Mikael Magnusson <mikachu@gmail.com>
To: Bart Schaefer <schaefer@brasslantern.com>
Cc: Zsh Users <zsh-users@zsh.org>
Subject: Re: backreferences
Date: Fri, 16 Oct 2015 06:11:16 +0200 [thread overview]
Message-ID: <CAHYJk3Q5OL807aE9eAw+jp2ueHFO7MPswYeqU0+n0ZUnG5JqgQ@mail.gmail.com> (raw)
In-Reply-To: <151015193032.ZM30783@torch.brasslantern.com>
On Fri, Oct 16, 2015 at 4:30 AM, Bart Schaefer
<schaefer@brasslantern.com> wrote:
> On Oct 15, 6:16pm, Ray Andrews wrote:
> } Subject: Re: backreferences
> }
> } if [[ "$sstring" = (#b)([(^(edcba))]*)(edcba)(*) ]];
>
> Umm, no. [(^(edcba))] is still a character class (open paren, caret,
> e,d,c,b,a, close paren). Just (^(edcba)) without the square brackets.
> And you have more parens then, so your $match[] indexes are wrong.
>
> if [[ "$sstring" = (#b)((^(edcba))*)(edcba)(*) ]]
>
> There are 5 sets of parens, and you care about $match[1], $match[4],
> and $match[5]. $match[2] is the prefix of $match[1] that was not
> consumed by the middle *, and $match[3] is an empty substring of
> $match[2] (because it was excluded from matching). Count off the
> open parens left to right to see this.
>
> In fact you don't even need the middle * because (^edcba) will eat
> an arbitrarily long string as long as it is not literally "edcba".
> So you can reduce this to
>
> if [[ "$sstring" = (#b)(^edcba)(edcba)(*) ]]
>
> and then you're back to only needing $match[1,3].
As a sidenote, (^foo)* is always useless to write, since (^foo) will
expand to the empty string, and then the * will consume anything else.
A useful way to think of (^foo) is a * that will exclude any matches
that don't match the pattern foo.
--
Mikael Magnusson
next prev parent reply other threads:[~2015-10-16 4:11 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-15 18:28 backreferences Ray Andrews
2015-10-15 23:16 ` backreferences Bart Schaefer
2015-10-16 1:16 ` backreferences Ray Andrews
2015-10-16 2:30 ` backreferences Bart Schaefer
2015-10-16 4:11 ` Mikael Magnusson [this message]
2015-10-16 4:27 ` backreferences Kurtis Rader
2015-10-16 5:42 ` backreferences Ray Andrews
2015-10-16 5:05 ` backreferences Bart Schaefer
2015-10-16 5:28 ` backreferences Bart Schaefer
2015-10-16 5:46 ` backreferences Ray Andrews
2015-10-16 11:14 ` backreferences Peter Stephenson
2015-10-16 5:36 ` backreferences Ray Andrews
2015-10-16 12:35 ` backreferences Bart Schaefer
2015-10-16 16:37 ` backreferences Ray Andrews
2015-10-17 3:33 ` backreferences Bart Schaefer
2015-10-17 5:16 ` backreferences Ray Andrews
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