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Re: Incorrect example for `[[` command.

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  Re: Incorrect example for `[[` command. hk <hkadeveloper@gmail.com> - 2019-09-21 20:47 +0800

#15389 — Re: Incorrect example for `[[` command.

Thanks. Have learnt a lot from your replies.

On Sat, Sep 21, 2019 at 5:34 PM Ilkka Virta <itvirta@iki.fi> wrote:

> On 21.9. 03:12, hk wrote:
> > Thanks for the reply. I was wrong in my report. It does match values like
> > aab and  aaaaaab  in its original form.
>
> In some systems, yes. (It does that on my Debian, but doesn't work at
> all on my Mac.)
>
> > It is syntatically correct as a regular expression.
>
> [[:space:]]*?(a)b  isn't a well-defined POSIX ERE:
>
>    9.4.6 EREs Matching Multiple Characters
>
>    The behavior of multiple adjacent duplication symbols ( '+', '*', '?',
>    and intervals) produces undefined results.
>
>
> https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/basedefs/V1_chap09.html
>
>
> --
> Ilkka Virta / itvirta@iki.fi
>

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