bug#41700: grep -v always exiting with 1 for empty file

[Andi Kleen]

On Thu, Jun 04, 2020 at 07:26:34PM +0900, Norihiro Tanaka wrote:
> 
> On Wed, 3 Jun 2020 20:26:41 -0700
> Andi Kleen <andi@firstfloor.org> wrote:
> 
> > 
> > % grep --version
> > grep (GNU grep) 3.4
> > ...
> > % echo -n > foo
> > % grep -v foo foo ; echo $?
> > 1
> > 
> > Would expect it to exit with zero in this case, since foo is not in the
> > file.
> > 
> > When the file is one byte it works as expected:
> > 
> > % echo > foo
> > % grep -v foo foo ; echo $?
> > 
> > 0
> > %
> 
> `0 if a line is selected, 1 if no lines were selected,' in manual.
> `0: One or more lines were selected. 1: No lines were selected.' in
> POSIX.
> 
> > % echo -n > foo
> > % grep -v foo foo ; echo $?
> 
> It returns no lines, so it seems reasonable to return 1.

I would argue that a empty file has a single empty line.

Besides it completely breaks the "is foo not in file" functionality.

In normal terminology that's a off by one bug. Why should 
an empty file be different than any other files?

I just had to rewrite a test script of mine and add lots of 

echo >> outputfile

statements to work around it.

-Andi