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From: Bob Bishop <rb@gid.co.uk>
In-Reply-To: <4C7260CC.9070407@list.mightyreason.com>
Date: Mon, 23 Aug 2010 13:45:26 +0100
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References: <4C7260CC.9070407@list.mightyreason.com>
To: chrisk-freebsd@list.mightyreason.com
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Cc: freebsd-current@freebsd.org, gabor@freebsd.org
Subject: Re: grep and Regular expression correctness
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Hi,

On 23 Aug 2010, at 12:51, chrisk-freebsd@list.mightyreason.com wrote:

> [...]The hardest part of POSIX regular expressions is in picking out the
> correct captured subexpressions.  This makes programs like "sed"
> vulnerable to the bad regex.h engine that comes with the operating system.
> 
> Luckily grep does not need the captured subexpressions, and thus does
> not need the complexity that comes from the ideas behind TRE. [etc]

I think grep does potentially need the captured subexpressions, for eg:

\([abc]\)99\1

matching eg b99b

--
Bob Bishop
rb@gid.co.uk