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Re: Incorrect example for `[[` command.
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From: |
Chet Ramey |
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Subject: |
Re: Incorrect example for `[[` command. |
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Date: |
Sun, 22 Sep 2019 13:53:37 -0400 |
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User-agent: |
Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 |
On 9/21/19 5:34 AM, Ilkka Virta 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.
It's ambiguous, but it can be interpreted as valid. I wonder why they used
"undefined" instead of the usual "unspecified."
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU chet@case.edu http://tiswww.cwru.edu/~chet/