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Re: dotgob+extglob bug


From: Chet Ramey
Subject: Re: dotgob+extglob bug
Date: Thu, 19 Jun 2014 10:09:11 -0400
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.6.0

On 6/9/14, 3:42 PM, Ian Kelling wrote:
> 
> Running this script with your own bash path demonstrates the bug.
> 
> #!/home/ian/opt/bash/bash --norc
> shopt -s extglob
> shopt -s dotglob
> cd $(mktemp -d)
> mkdir a
> touch a/.b
> touch a/c
> echo a/!(.b)
> 
> output:
> a/. a/.. a/c
> 
> this happens with all bash versions 4.3+ (latest is patch 18).

Yes, it's an interesting question: what exactly does pattern negation
include?  You can match all filenames beginning with a `.' by using `.'
as the first character of the pattern, so should a negated pattern
beginning with a `.' match all filenames beginning with a `.' that don't
match that particular pattern?  The bash-4.3 implementation says yes.
(FWIW, ksh93 disagrees.)

> before that, the output is:
> 
> a/c

Yes, bash-4.2 had real problems with pattern negation (all extglob
patterns, really) and files beginning with `.'.  So much so that it
failed to generate any matches for *(.*), which is just totally wrong.

> Another related bug. man bash states:
> 
> The file names ``.''  and ``..''  are always ignored
>        when GLOBIGNORE is set and not null.
> 
> Which clearly implies that . and .. should not be ignored in some other
> case. 

Sure. One is that they're not ignored when the pattern begins with a `.'.
For instance, using .* as the pattern with the above directory contents
expands to ". .. .b c".

> Well, that was not true before 4.3

Absolutely it was true before bash-4.3.

, but I'm guess this new
> behavior is a bug, and the doc is a bug, since the doc hasn't changed,
> and setting GLOBIGNORE doesn't actually make . and .. be ignored.

Of course it does.  When GLOBIGNORE is set to something that's not a null
value (say, GLOBIGNORE=a) , echo .* in a directory with the contents as
above expands to ".b c", echo !(.*) expands to "c", and echo *(.*) expands
to ".b".

Chet
-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    address@hidden    http://cnswww.cns.cwru.edu/~chet/



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