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Date: Thu, 7 Dec 2017 01:08:01 +0000
From: Ken Moffat <zarniwhoop@ntlworld.com>
To: RW <rwmaillists@googlemail.com>
Cc: freebsd-questions@freebsd.org
Subject: Re: grep problem
Message-ID: <20171207010801.GA10604@milliways.localdomain>
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On Thu, Dec 07, 2017 at 12:55:42AM +0000, RW via freebsd-questions wrote:
> 
> Can anyone explain why '-' needs escaping in the following. What
> special meaning does it have outside of []? 
> 
> $ echo 'a-b' | grep  'a-b'
> a-b
> 
> $ echo 'a-b' | grep  '-b'
> Usage: grep [OPTION]... PATTERN [FILE]...
> Try `grep --help' for more information.
> 
> $ echo 'a-b' | grep  '\-b'
> a-b
> 
In gnu grep, '-' indicates it should read from STDIN, I assume that
FreeBSD's grep is the same.

ĸen
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