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From: Chet Ramey <chet.ramey@case.edu>
Newsgroups: gnu.bash.bug
Subject: Re: Incorrect example for `[[` command.
Date: Sat, 21 Sep 2019 17:15:19 -0400
Organization: ITS, Case Western Reserve University
Lines: 23
Approved: bug-bash@gnu.org
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On 9/20/19 8:12 PM, hk wrote:

> What is wrong is the description `zero or one instances of 'a''. But if we
> correct the right hand side word to be  `[[:space:]]*(a)?b' that it does
> match what the description says.(the parenthese around `a' could be omitted).

Yeah, that's the typo.

> I was also wrong saying it was a pattern instead of a regular expression.
> It is syntatically correct as a regular expression.

That's true. According to the POSIX ERE definition, the `?' is a special
ERE character in an invalid position (it's only special after a specifier
that matches a single character, not after a separate specifier that
matches multiple characters), so it matches itself.

Chet

-- 
``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/