cat /proc/fs/nfs/exports

exportfs

#  if [ ! -r /etc/exports ]; then # no config file, exit:
#    exit
#  elif ! grep -v '^#' /etc/exports | grep '/' 1> /dev/null 2> /dev/null ; then
#    exit # no uncommented shares in /etc/exports
#  fi

df -a | grep -wq '/usb$' || {   # proceed if not mounted, /usb is my mountpoint
   usbid="xxxxxxxxxxxxxxxxxxxxxxxxx"   # whatever is the blkid of the usb-disk
   usbdev="$(blkid -U $usbid)" || usbdev=""
   test "x$usbdev" = x || {    # so it's present :-)
      if mount -o rw,noatime $usbdev /usb; then echo ":: $usbdev mounted on /usb ..."
      else echo "-- failure mounting $usbdev ..."; fi
   }
   unset usbid usbdev   # the environmentalists are gonna luv me!
}

df -a | grep -wq '/usb$' && {   # ok, it _is_ mounted
   ok=no
   exportfs | ( while read a b; do
      test "x$a" = x/usb && { ok=yes; break; }
   done )
   test $ok = no && {   # not exported, so do it
      exportfs -iv -o rw,insecure,no_root_squash 192.168.1.0/24:/usb
   }
   unset ok
}