find . -type f > /tmp/filelist
while read file; do
    if ! fgrep "$file" incomplete.sha256; then
        echo "$file"
        sha256sum "$file" >> incomplete.sha256
    fi
done < /tmp/filelist

find . -type f > /tmp/filelist
while read file; do
    if ! fgrep "$file" incomplete.check; then
        echo "$file"
        c=$(mktemp)
        grep "$file" complete.sha256 > $c
        sha256sum -c $c >> incomplete.check
        rm $c
    fi
done < filelist