1. Prerequisites: Android device must be rooted, busybox is required
2. Download curl Android binary from here: https://curl.haxx.se/download.html
3. As root, put curl binary into /system/bin/ and ca-bundle.crt into /system/usr/ and execute chmod 0755 /system/bin/curl
4. Put dropbox_uploader.sh into /mnt/sdcard/dropbox_uploader
5. Make changes to dropbox_uploader.sh
6. Home directory defaults to /data in Android, which is non-writable by non-root users, so change CONFIG_FILE variable to /mnt/sdcard/dropbox_uploader/.dropbox_uploader
7. Configure TMP_DIR, e.g. /mnt/sdcard/dropbox_uploader/tmp
8. curl won't find ca cert bundle by itself, so point it to the right place via CURL_ACCEPT_CERTIFICATES="--cacert /system/usr/ca-bundle.crt"
9. Busybox stat command does not support output formating. As a workaround, file_size function must be changed into

function file_size
{
  a=(`stat -t "$1"`)
  echo ${a[1]}
  return
}

Finally, dropbox_uploader can be set up by executing "bash /mnt/sdcard/dropbox_uploader/dropbox_uploader.sh" via Android terminal or adb shell as a non-root user.