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Date: Thu, 7 Dec 2017 00:55:42 +0000
From: RW <rwmaillists@googlemail.com>
To: freebsd-questions@freebsd.org
Subject: grep problem
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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