linux-kernel - Re: mmotm 2019-07-04-15-01 uploaded (gpu/drm/i915/oa/)

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Date:   Thu, 04 Jul 2019 22:22:41 -0700
From:   Joe Perches <joe@...ches.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Mark Brown <broonie@...nel.org>, linux-fsdevel@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        mhocko@...e.cz, mm-commits@...r.kernel.org,
        Michal Wajdeczko <michal.wajdeczko@...el.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Intel Graphics <intel-gfx@...ts.freedesktop.org>,
        DRI <dri-devel@...ts.freedesktop.org>,
        Chris Wilson <chris@...is-wilson.co.uk>
Subject: Re: mmotm 2019-07-04-15-01 uploaded (gpu/drm/i915/oa/)

On Thu, 2019-07-04 at 22:09 -0700, Andrew Morton wrote:
> diff(1) doesn't seem to know how to handle a zero-length file.
> 
> y:/home/akpm> mkdir foo
> y:/home/akpm> cd foo
> y:/home/akpm/foo> touch x
> y:/home/akpm/foo> diff -uN x y
> y:/home/akpm/foo> date > x
> y:/home/akpm/foo> diff -uN x y
> --- x   2019-07-04 21:58:37.815028211 -0700
> +++ y   1969-12-31 16:00:00.000000000 -0800
> @@ -1 +0,0 @@
> -Thu Jul  4 21:58:37 PDT 2019
> 
> 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