How to physically reorder files `03.mp3 01.mp3 02.mp3` (`ls -f`) in a directory?

Question

The physical order of the files matters when I copy them onto my USB stick and listen in car mp3 player. Most of my music album folders are unsorted, e.g. ls -f may produce:
03.song3.mp3
01.song1.mp3
02.song2.mp3

When I copy that folder onto my USB stick, the files get copied in that order. My car mp3 player displays the files in the unsorted order, which is not what I want. I can subsequently reorder the files on the USB stick (see: How to reorder folders? (as displayed in `ls -U`)), but could avoid that altogether if I could reorder them within that directory them on my hard drive (ext4)? Is there a way of doing that?

(Failing that, there might be a way of writing a find command, that gets the files, sorts them, and then copies them in order??) Any suggestions?

Answer 1

It's unlikely that you'll be able to do this on ext4. Unlike FAT(32), which used a linear table of files in a directory, modern filesystems use complex structures such as B+tree (NTFS, XFS) or hashed B-tree (ext3/4), where all entries are sorted according to a specific algorithm.

In particular, ext3/4 sorts files according to the hash value of their name, so you always get the same files in the same order. It's possible to disable the dir_index feature via tune2fs, but it might cost you performance if you have directories containing many files.

---

A very basic command for this could be cp dir/* otherdir/, where the shell sorts names when expanding arguments, and cp simply copies them in the order given.

Something more complex, for copying subdirectories:

#!/usr/bin/env bash
srcdir=$1
destdir=$2

find "$srcdir" \( -type d -printf "0dir %P\0" \) \
            -o \( -type f -printf "1file %P\0" \) |
sort -z | while read -r -d '' type path; do
    case $type in
        "0dir") mkdir -vp "$destdir/$path";;
        "1file") cp -v "$srcdir/$path" "$destdir/$path";;
    esac
done