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Re: + vs. [^/]* - Regular Expression bug?


From: DennisW
Subject: Re: + vs. [^/]* - Regular Expression bug?
Date: Tue, 9 Feb 2010 21:18:47 -0800 (PST)
User-agent: G2/1.0

On Feb 8, 11:38 pm, Morten Lauritsen Khodabocus <address@hidden>
wrote:
> Hello,
>
> Ran into some particular behaviour with REs in bash, I just cannot
> understand how this could possibly be correct behaviour. Then again, I
> am no bash guru, could very well be me missing a clue.
>
> If I am wasting your time, sincere apologies.
>
> I am not subscribed to the list, so please include my email explicitly
> in any replies that you would like me to read / respond to.
>
> Thanks a million for a great shell! Beers are on me next time any of you
> are in Zurich.
>
> Here's the bashbug description:
>
> Configuration Information [Automatically generated, do not change]:
> Machine: i486
> OS: linux-gnu
> Compiler: gcc
> Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='i486'
> -DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='i486-pc-linux-gnu'
> -DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash'
> -DSHELL -DHAVE_CONFIG_H   -I.  -I../bash -I../bash/include
> -I../bash/lib   -g -O2 -Wall
> uname output: Linux sony2 2.6.31-19-generic #56-Ubuntu SMP Thu Jan 28
> 01:26:53 UTC 2010 i686 GNU/Linux
> Machine Type: i486-pc-linux-gnu
>
> Bash Version: 4.0
> Patch Level: 33
> Release Status: release
>
> Description:
> Two regular expressions should match the same thing, but for some reason
> do not:
> [[ '/home/' =~ [^/]+ ]]; echo address@hidden
> and
> [[ '/home/' =~ [^/]* ]]; echo address@hidden
> the first matches 'home', the second matches nothing. The only
> difference is * vs. + AFAICT, both expressions should match 'home'.
>
> Repeat-By:
> Simply evaluate the two lines from the description.
>
> Thanks again,
> Morten

* means zero or more characters. It found zero and stopped. You could
do:

[[ '/home/' =~ /([^/]*) ]]; echo ${BASH_REMATCH[1]}


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