GNU bug report logs - #41700
grep -v always exiting with 1 for empty file

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Message #29 received at 41700 <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: Paul Eggert <eggert <at> cs.ucla.edu>, Andi Kleen <andi <at> firstfloor.org>
Cc: 41700 <at> debbugs.gnu.org
Subject: Re: bug#41700: grep -v always exiting with 1 for empty file
Date: Thu, 4 Jun 2020 15:34:18 -0500

On 6/4/20 3:27 PM, Paul Eggert wrote:
> On 6/4/20 12:30 PM, Andi Kleen wrote:
> 
>> in your definition would
>>
>> echo -n foo > file
>>
>> (so no newline, but non zero length)
> 
> No, the file has zero length:
> 
> $ echo -n >file

You missed the 'echo -n foo' that prints 3 bytes to file.

> $ ls -l file
> -rw-r--r-- 1 eggert eggert 0 Jun  4 13:24 file
>> have one or zero lines?
> 
> Empty files have no lines.
> 
> On 6/4/20 1:13 PM, Eric Blake wrote:
>> The most intuitive behavior is that grep behaves as if the file included the
>> trailing newline
> 
> That's what grep does with files that end in a non-newline byte; such files are
> also not text files so POSIX does not specify the behavior.

I answered the question about the 3-byte file.  The 0-byte file _IS_ a 
text file, consisting of zero lines.

> But grep, like other
> GNU tools, treats empty files as if they contain no lines; this matches most
> people's intuition.

POSIX actually requires this behavior for an empty file.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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