How do I delete all of a set of files in a random order?

Question

I have a set of files, all that are named with the convention file_[number]_[abcd].bin (where [number] is a number in the range 0-size of drive in MB). i.e there is file_0_a.bin, file_0_b.bin, file_0_c.bin and file_0_d.bin and then the 0 would become a 1 and so on.

The number of files is figured out at run-time based on the size of the partition. I need to delete all of the files that have been created, but in a pseudo-random manner. in blocks of size that I need to be able to specify, i.e where there is 1024 files, delete 512, then delete another 512.

I have the following function for doing it currently, which I call the required number of times, but it will get progressively less likely to find a file that exists, to the point where it might never complete. Obviously, this is somewhat less than ideal.

What is another method that I can use to delete all of the files in a random order?

deleteRandFile() #$1 - total number of files
{
    i=$((RANDOM%$1))
    j=$((RANDOM%3))
    file=""

    case $j in
    0)
        file="${dest_dir}/file_${i}_a.bin";;
    1)
        file="${dest_dir}/file_${i}_b.bin";;    
    2)
        file="${dest_dir}/file_${i}_c.bin";;
    3)
        file="${dest_dir}/file_${i}_d.bin";;
    esac

    if ! [[ -f $file ]]; then
        deleteRandFile $1
    else
        rm $file
    fi

    return 0;
}

Edit: I'm trying to delete in random order so that I can fragment the files as much as possible. This is part of a script that begins by filling a drive with 1MB files, and deletes them, 1024 at a time, then fills the 'gap' with 1 1GB file. Rinse and repeat until you have some very fragmented 1GB files.

Answer 1

If you want to delete all the files, then, on a GNU system, you could do:

cd -P -- "$destdir" &&
  printf '%s\0' * | # print the list of files as zero terminated records
    sort -Rz |      # random sort (shuffle) the zero terminated records
    xargs -r0 rm -f # pass the input if non-empty (-r) understood as 0-terminated
                    # records (-0) as arguments to rm -f

If you want to only delete a certain number of those matching a regexp you'd insert something like this between the sort and xargs:

awk -v RS='\0' -v ORS='\0' -v n=1024 '/regexp/ {print; if (--n == 0) exit}'

With zsh, you could do:

shuffle() REPLY=$RANDOM
rm -f file_<->_[a-d].bin(.+shuffle[1,1024])

Answer 2

Here's a potential alternative using find and shuf:

$ find $destdir -type f | shuf | xargs rm -f

This will find all the files in $destdir and then use the shuf command to shuffle their order, and then pass the list on to xargs rm -f for deletion.

To gate how many files are deleted:

$ find $destdir -type f | shuf | head -X | xargs rm -f

Where -X is the number of files that you want to delete, for example, head -100.