Re: [PATCH] ls: add --files0-from=FILE option

[Pádraig Brady]

On 19/04/2021 18:08, Carl Edquist wrote:
> Greetings Coreutils,
>
> I'm submitting for your consideration here a patch to add the standard
> '--files0-from=FILE' option to ls.
>
> (To read NUL-terminated names from FILE rather than using command line
> arguments.)
>
>
> Motivation for adding this to ls is mainly to let ls sort arbitrarily many
> items, though it is also necessary for getting the correct aggregate
> column widths to align long format (-l) output across all file names.
>
>
> As a real example, if you want to use ls to list (say, in long format with
> human sizes) all the sources in the linux kernel tree according to size,
> you might naively try one of
>
>      [linux]$ find -name '*.[ch]' -exec ls -lrSh {} +
>      [linux]$ find -name '*.[ch]' -print0 | xargs -0 ls -lrSh
>
> but you'll see the sizes spiral over and over, finally ending somewhere in
> the middle:
>
> ...
> -rw-r--r-- 1 kx users  81K Apr 15 04:30 ./arch/arm/boot/dts/imx6sll-pinfunc.h
> -rw-r--r-- 1 kx users  83K Apr 15 04:30 ./arch/arm/boot/dts/imx6dl-pinfunc.h
> -rw-r--r-- 1 kx users  87K Apr 15 04:30 ./arch/arm/mach-imx/iomux-mx35.h
> -rw-r--r-- 1 kx users 107K Apr 15 04:30 ./arch/arm/boot/dts/imx7d-pinfunc.h
> -rw-r--r-- 1 kx users 143K Apr 15 04:30 ./arch/arm/boot/dts/imx6sx-pinfunc.h
>
>
> In this case, xargs batches *13* separate invocations of ls; so the
> overall sorting is completely lost.
>
> But with the new option:
>
>      [linux]$ find -name '*.[ch]' -print0 | ls -lrSh --files0-from=-
>
> The sizes all scroll in order

One can also implement this functionality with the DSU pattern like:

  nlargest=10
  find . -printf '%s\t%p\0' |
  sort -z -k1,1n | tail -z -n"$nlargest" | cut -z -f2 |
  xargs -r0 ls -lUd --color=auto --

Arguably that's more scalable as the sort operation will not
be restricted by available RAM, and will use temp storage.

Also it's more robust as ls is the last step in the pipeline,
presenting the files to the user. If you wanted the largest 10
with ls --files0-from then file names containing a newline
would mess up further processing by tail etc.

> Similarly, say you would like to view / scroll through your extensive mp3
> collection in chronological order (based on when you added the files to
> your collection).  You can do it now with the new option:
>
>      [music]$ find -name \*.mp3 -print0 | ls -lrth --files0-from=-

I've used a https://www.pixelbeat.org/scripts/newest script
for a long time with similar find|xargs technique as I described above.

In saying all of the above, I do agree though that for consistency
commands that need to process all arguments with global context,
should have a --files0-from option.
Currently that's du and wc for total counts, and sort(1) for sorting.
Since ls has sorting functionality, it should have this option too.

thanks!
Pádraig