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Date: Fri, 30 Aug 2019 10:44:00 +0300
From: Andrey Repin <anrdaemon AT yandex DOT ru>
Reply-To: cygwin AT cygwin DOT com
Message-ID: <42748516.20190830104400@yandex.ru>
To: Eliot Moss <moss AT cs DOT umass DOT edu>, cygwin AT cygwin DOT com
Subject: Re: bug with grep 3.0.2 in cygwin 3.0.7
In-Reply-To: <806ab587-a07c-1616-1486-ebb258ace1d9@cs.umass.edu>
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Greetings, Eliot Moss!

>>> I encounter some problem with grep option -E on cygwin 3.0.7
>> 
>> 
>>> echo "a^b" | grep "a^b" #answer a^b ie it's OK
>>> but
>>> echo "a^b" | grep -E "a^b" #answer nothing " for me it's KO
>> 
>> That's an expected result of an impossible constraint.
>> 
>>> I have to backslash ^ to be OK like : grep -E 'a\^b'
>> 
>> Yes.
>> 
>>> Is-it a bug ?
>> 
>> No.
>> 
>>> I don't know if all versions of cygwin and grep are concerned.
>> 
>> RTFM, this is regexp basics.

> There was a really great answer to this earlier.  I tried an
> answer, but was wrong.  One has to read the "fine print" really
> carefully.  At first I thought it was a bug, at least in the
> documentation, but the meaning of a^b, when ^ is the metacharacter,
> is kind of subtle (IMO at least).  It's easy to miss that
> subtlety and think that if ^ is not at the beginning of an
> expression it will be treated as an ordinary character ...

> But my main point is that RTM would be enough; RTFM seemed
> to me perhaps a little more rude than necessary.

Adding to the earlier answers (sorry, replying on the road is not efficient),
there's a https://www.regular-expressions.info/
Which contains a great deal of information about RE, their kinds, caveats and
implementations in various languages.


-- 
With best regards,
Andrey Repin
Friday, August 30, 2019 10:42:35

Sorry for my terrible english...


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