grep problem

[Yuri Pankov]

On Thu, Dec  7, 2017 at 00:55:42AM +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

Looks like it's treated as option -b even inside the single quotes, you 
could use '--' to mark the end of options, i.e.:

$ echo 'a-b' | grep -- -b
a-b