This script scans for connected usb media, selects the first one and creates a playlist from the USB's top-level directory. Connect to the same network as the raspberry pi and scp the script to /home/osmc/.kodi/userdata (this may vary depending on OS). This is meant for a Raspberry Pi used as a media player, with OSMC installed.

autoexec.py

# Autoplay videodirectory
import os, xbmc, time

usb_dir  = "/media" # path of external media
delay    = 10       # seconds to delay media player

# Collect directories (USBs) in usb directory
usb_list = []
for fname in os.listdir(usb_dir):
  fpath = os.path.join(usb_dir, fname)
  if os.path.isdir(fpath):
    usb_list.append(fpath)

usb_list.sort()
path = usb_list[0]

dir_list = os.listdir(path)
dir_list.sort()

video_list = xbmc.PlayList(xbmc.PLAYLIST_VIDEO)
video_list.clear()

for fname in dir_list:
  video_list.add(path + "\\" + fname)

# shuffle playlist
# video_list.unshuffle()

# put playlist on repeat
xbmc.executebuiltin("xbmc.playercontrol(RepeatAll)")

# delay play
time.sleep(delay)

# play playlist
xbmc.Player().play(video_list)

autoexec_to_pi.sh

scp -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -q ./autoexec.py osmc@192.168.43.132:/home/osmc/.kodi/userdata