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Date:   Thu, 4 Jul 2019 22:29:06 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Joe Perches <joe@perches.com>
Cc:     Stephen Rothwell <sfr@canb.auug.org.au>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Mark Brown <broonie@kernel.org>, linux-fsdevel@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-mm@kvack.org,
        Linux-Next Mailing List <linux-next@vger.kernel.org>,
        mhocko@suse.cz, mm-commits@vger.kernel.org,
        Michal Wajdeczko <michal.wajdeczko@intel.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Intel Graphics <intel-gfx@lists.freedesktop.org>,
        DRI <dri-devel@lists.freedesktop.org>,
        Chris Wilson <chris@chris-wilson.co.uk>
Subject: Re: mmotm 2019-07-04-15-01 uploaded (gpu/drm/i915/oa/)
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On Thu, 04 Jul 2019 22:22:41 -0700 Joe Perches <joe@perches.com> wrote:

> > So when comparing a zero-length file with a non-existent file, diff
> > produces no output.
> 
> Why use the -N option ?
> 
> $ diff --help
> [...]
>   -N, --new-file                  treat absent files as empty
> 
> otherwise
> 
> $ cd $(mktemp -d -p .)
> $ touch x
> $ diff -u x y
> diff: y: No such file or directory

Without -N diff fails and exits with an error.  -N does what's desired
as long as the non-missing file isn't empty.