Re: Bug: grep behaves incorrectly under the locale C.UTF-8, if a file contains Umlaut characters

[Erik Bray <erik.m.bray@gmail.com>]

On Wed, May 24, 2017 at 9:52 AM, Ronald Fischer wrote:
> I have a file X which contains ASCII text, but also in some lines German
> umlaut characters. The file is classified as:
>
>      $ file X
>      X: ISO-8859 text, with CRLF line terminators
>
> If I grep the file using, say,
>
>      $ grep  .  X  >Y
>
> (i.e. select every non-empty line and write the result to Y), this works
> fine, if LANG is set to one of: UTF-8, C, C.de_DE, C.en_EN, en_EN,
> de_DE.
>
> However, if LANG is set to C.UTF-8, two things happen:
>
> - grep classifies the file as binary file and produces the error message
> "Binary file X matches"
>
> - Both the grepped lines (i.e. in our example the non-empty lines) AND
> the error message end up in the standard output (i.e. in file Y).
>
> IMO, there are several problems with this:
>
> 1. It's hard to see, why an umlaut character makes the file X binary
> under encoding C.UTF-8, but not under encoding UTF-8 or C.en_EN

Only one of these, "UTF-8", specifies an *encoding*.  Further, I don't
think just "UTF-8" or "C.en_EN" are valid locale specifiers.  You can
read more about how Cygwin handles locales here:

https://cygwin.com/cygwin-ug-net/setup-locale.html

Certainly, if you set something like LANG="C.UTF-8" it will use UTF-8
to decode the text in the file and, failing that, treat it as binary.
If you know it's ISO-8859-1 you can use either LANG= or
LC_CTYPE="C.ISO-8859-1".  Or, if you know the language, you should be
able to use LC_CTYPE="de_DE".  Each language+territory has a default
encoding associated with it.  For German I think it is one of the
ISO-8859-* variants.  Or you can use the variant "de_DE@euro" which
forces ISO-8859-15 which includes the euro symbol, among other
possibilities.  So I think your main problem here is just not
specifying your locale correctly.

> 2. If grep classifies a file as binary, I think the desired behaviour
> would be to NOT produce any output, unless the -a flag has been
> supplied.
>
> 3. If grep writes a message "Binary file ... matches", this message
> should go to stderr, not stdout. The stdout is supposed to contain only
> a subset of the input lines.

I would tend to agree with this, but this is normal behavior of grep
(on Linux too), so I would take it up with the authors of grep.

Best,
Erik

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