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From: Ilkka Virta <itvirta@iki.fi>
Newsgroups: gnu.bash.bug
Subject: Re: Incorrect example for `[[` command.
Date: Sat, 21 Sep 2019 22:15:05 +0300
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On 21.9. 21:55, Dmitry Goncharov wrote:
> On Sat, Sep 21, 2019 at 12:34:39PM +0300, Ilkka Virta wrote:
>> [[: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
> 
> This is unfortunate.
> *? and +? are widely used not greedy regexes.

In Perl-compatible regexes. Bash uses POSIX extended regular expressions.

And on a GNU system, while *? and +? don't give errors when used in an 
ERE, they still don't make the repetition non-greedy. They just act the 
same as a single * (as far as I can tell anyway).

  bash$ re='<.+?>'
  bash$ [[ "a<b>c<d>e" =~ $re ]] && echo $BASH_REMATCH
  <b>c<d>
  bash$ [[ "a<>e" =~ $re ]] && echo $BASH_REMATCH
  <>

-- 
Ilkka Virta / itvirta@iki.fi