How to set the number of moved files?

Question

I'm moving png files from source/ to dest/ with this:

mv /source/*.png /dest/

How can I change that command so I only move 10 png files?

Specify the correct file name pattern, maybe? What about ls | head -10? — U. Windl, Dec 02 '22 at 07:16
@cas I know how to do that correctly, but I wanted the OP to explain a bit more what he really wants to do, or what the real problem is. — U. Windl, Dec 02 '22 at 07:47
so why suggest parsing ls? that's just irresponsible, especially if you claim to know better. — cas, Dec 02 '22 at 07:56

score 4 · Accepted Answer · edited Dec 02 '22 at 10:48

You can do this in Zsh with a glob qualifier:

mv /source/*.png([1,10]) /dest/

Moves the first 10 ones in alphabetic order. You can pick a different order using the o/O/n qualifiers. For instance:

mv /source/*.png(OL[1,10]) /dest/

Would move the 10 largest ones.

An optimised version that selects the first 10 matches without bothering to sort can be done with the Y qualifier:

mv /source/*.png(Y10) /dest/

score 4 · Answer 2 · answered Dec 02 '22 at 10:53

POSIXly, that could be done with:

set -- /source/*.png
[ "$#" -le 10 ] || shift "$(( $# - 10 ))"
mv -- "$@" /dest/

Which would move the 10 last ones in alphabetic order.

Note that it excludes hidden ones and if there's no match, it would attempt to move a file called /source/*.png and likely fail.

Hobber · Answer 3 · 2022-12-02T07:51:34.197

-1

ls /source/*.png | head -n10 | xargs -I{} mv {} /dest/

edited Dec 02 '22 at 07:51

answered Dec 02 '22 at 07:35

Hobber

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This is only safe if you're using a recent version of GNU ls with the --zero option, combined with head -z -n 10, and xargs -0r .... And, since everything else relies on GNU versions, you may as well use GNU mv's -t option too. ls --zero /source/*.png | head -z -n 10 | xargs -0r mv -t dest/. Even so, it's still better to use find: find /source -maxdepth 1 -name '*.png' -print0 | head -z -n 10 | xargs -0r mv -t dest/. – cas Dec 02 '22 at 07:43
@cas so using ls --zero avoids the problem of never parse ls? I have no idea about --zero and how that works but with your example I understood better. – Edgar Magallon Dec 02 '22 at 16:13
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@EdgarMagallon --zero is fairly new for GNU ls (first added as --null in July 2021, renamed to --zero a few days later. BTW, according to the changelog, "--zero also implies -1, -N, --color=none, --show-control-chars"). I wouldn't say "avoids the problem" - won't help at all for parsing metadata out of ls -l (that's what stat is for, anyway) but should be OK for just generating a list of NUL-separated files to pipe into other programs or read into an array with mapfile. Personally, I'll stick with using find, although the convenience of ls's sorting capabilities might be useful. – cas Dec 02 '22 at 16:53
@cas thanks for the explanation! That's very clear and useful. I will take a look at the manuals too. As you said it'll be better keep using find or for in /somepath too – Edgar Magallon Dec 02 '22 at 17:50

How to set the number of moved files?

3 Answers3