Bash script to continuously watch for output files and move them

mv_files.sh

#!/usr/bin/env bash
log=mv_files.log
spare=/spare/ryan
dest=/cb/data/imagenet1k2/new/
while true; do
    if test -n "$(shopt -s nullglob; echo $spare/*)"
    then
        echo "Moving files to $dest"
        echo "Moving files to $dest" >> $log
        ls -rt1 $spare | head -n -10 | xargs -n 1 echo
        ls -rt1 $spare | head -n -10 | xargs -n 1 echo >> $log
        ls -rt1 $spare | head -n -10 | xargs -I {} mv $spare/{} $dest
    else
        echo "$spare is empty"
        echo "$spare is empty" >> $log
    fi
    echo "Sleeping..."
    echo "Sleeping..." >> $log
    sleep 1800  ## 1800 s = 30 mins
done