Here is a python script that does as you described.

For convenience reasons, to be used with other conversion commands, I defined the filepath+name and the destination before entering it in the convert command. That also makes it easy to change the destination to something else than the file's current directory (if for some reason you might need that).

note: In some cases (like mine), the command

libreoffice --headless --convert-to xls

only works when using sudo. If that is the case, you need to change ownership of ~/.config with the command:

sudo chown -R --reference="$HOME" ~/.config

as described here.

The script:

#!/usr/bin/python3



convert_dir = "/path/to/folder/tobeconverted"

import os

import subprocess



for root, dirs, files in os.walk(convert_dir):

    for name in files:

        if name.endswith(".xlsx"):

            # filepath+name

            file = root+"/"+name

            destination = root

            subprocess.Popen(["libreoffice", "--headless", "--convert-to", "xls", file, "--outdir", destination])

        else:

            pass

Copy it into an empty textfile, replace the directory in the top of the file, save it with the .py extension and run it with the command:

python3 /path/to/scrip/script.py

But I am pretty sure you know that. :)