Date: Sun, 26 Jun 2016 16:34:11 +0200 From: Polytropon <freebsd@edvax.de> To: =?UTF-8?B?RGFuacOrbA==?= de Kok <me@danieldk.eu> Cc: freebsd-questions@freebsd.org Subject: Re: grep and anchoring Message-ID: <20160626163411.d05f863e.freebsd@edvax.de> In-Reply-To: <20232C89-B821-41EC-9188-C2A19C679BD8@danieldk.eu> References: <20232C89-B821-41EC-9188-C2A19C679BD8@danieldk.eu>
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On Sun, 26 Jun 2016 15:10:57 +0200, Daniël de Kok wrote:
> Dear all,
>
> After a BSD hiatus of many years, I am tinkering with FreeBSD again.
> I’ve run into some strange issue with grep and beginning of line (^)
> anchoring:
>
> —
> % echo "1234 1234 1234" | egrep -o '^….'
> 1234
> 123
> 4 12
> % echo "123412341234" | egrep -o '^....'
> 1234
> 1234
> 1234
> —
>
> Any idea what is going on here?
I think what you see here is a typical "UTF-8 fsck-up".
The first search pattern contains a an ellipsis ("…",
2 bytes long, representing 3 characters), and a single
dot (".", one byte long, 1 character); the second pattern
contains four dots (4 x ".", 1 byte long, 1 character).
Of course grep interprets "…" and "..." differently.
In my mailer, I can see the difference clearly as the
ellipsis … is displayed in monospace font as a _one_
character wide symbol on the screen.
Or is this just an "enrichment" your MUA added? :-)
I'm quite sure you run into similar problems when you
include ligatures (like st, ft, ffi, ck or the like)
or one of the many different hyphend and spaces in a
search pattern. :-)
Otherwise, your example seems to show the expected
behaviour.
% echo "1234 1234 1234" | egrep -o '^....'
1234
123
4 12
% echo "123412341234" | egrep -o '^....'
1234
1234
1234
First 4-character pattern is "1234", next is " 123",
and last is "4 12" (each 4 characters wide, as the
space character " " is also "any character" that matches
the . pattern). In the second example, the groups match
4 characters each ("1234" x 3).
What different results did you expect? Or am I misinterpreting
your question?
--
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...
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