diff(1) -N behaviour - Bug 233402

[Chris]

On Wed, 27 May 2020 11:06:52 +0200 Baptiste Daroussin bapt at FreeBSD.org said

> On Wed, May 27, 2020 at 08:52:38PM +1200, Fehmi Noyan ISI via freebsd-hackers
> wrote:
> > 
> > 
> > > On 23/05/2020, at 11:47 PM, Yuri Pankov <ypankov at fastmail.com> wrote:
> > > 
> > > Fehmi Noyan ISI via freebsd-hackers wrote:
> > >>> On 23/05/2020, at 11:21 PM, Yuri Pankov <ypankov at fastmail.com> wrote:
> > >>> 
> > >>> Fehmi Noyan ISI via freebsd-hackers wrote:
> > >>>> Hiya
> > >>>> Apparently, after we switched from GNU diff to BSD diff, the -N flag no
> > longer assumes absent files as empty.
> > >>>> There is a bug report about GNU diff compatibility but when I look at
> > diff(1) man page, I see that not treating absent files as empty is intentional
> > rather than a missing functionality.
> > >>>> If this is not the case, I can work on patch to match to GNU diff
> > behaviour, otherwise, this bug report can be closed I think.
> > >>>> What’s your take on this?
> > >>>> -N --new-file
> > >>>>     If a file is found in only one directory, act as if it was found
> > >>>>     in the other directory too but was of zero size.
> > >>>> man for GNU diff
> > >>>> -N, --new-file
> > >>>>     treat absent files as empty
> > >>> 
> > >>> I think both descriptions say the same, i.e. "zero size" == "empty”?
> > >> Maybe it’s my interpretation, but if you do not supply the second
> > argument to diff(1), it complains
> > >> $ echo “test” > a.txt
> > >> $ diff -N a.txt nofile
> > >> diff: nofile: No such file or directory
> > >> $
> > >> GNU diff assumes an empty file for the missing second file and makes the
> > comparison
> > >> $ echo “test” > a.txt
> > >> $ diff -N a.txt nofile
> > >> 1d0
> > >> < test
> > >> $
> > > 
> > > I must admit that I never used -N without -r, so it's probably the only
> > case that needs fixing?
> > > 
> > > $ mkdir a b
> > > $ echo bar > a/foo
> > > $ diff -ruN a b
> > > diff -ruN a/foo b/foo
> > > --- a/foo       2020-05-23 14:44:34.525932000 +0300
> > > +++ b/foo       1970-01-01 03:00:00.000000000 +0300
> > > @@ -1 +0,0 @@
> > > -bar
> > > 
> > 
> > Took me a while to reply…
> > With -N, GNU diff does not give an ENOENT
> > 
> > % echo foo > bar
> > % diff bar nofile.txt
> > diff: nofile.txt no such file or directory
> > % diff -N bar nofile.txt
> > 1d0
> > < foo
> > 
> > Do we want BSD diff do the same, i.e. match the -N functionality of GNU
> > diff?
> > 
> Yes we do,
Why? If someone wants a GNU diff. Can't they simply install it? If
FreeBSD diff is to become like GNU diff, what's the point of having
a FreeBSD version.
Apologies in advance if I'm missing anything here.

Thanks.

--Chris
> if you do provide a patch I would be more than happy to review
> and
> apply it.
> 
> Best regards,
> Bapt