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
