Move Files From One Folder To Another In UNIX

There are around 13 files in folder1.I need to move these files to another folder folder2,one file at a time, after checking whether a file exists in another folder folder3.

If a file exists in folder3, we should not move files from folder1 to folder2.
If there are no files in folder3, we need to move the first file from folder1 to folder2.
Again, we need to check if a file exists in folder3 before moving the second file from folder1 to folder2.

Please help me with this.

for FILE in folder1/*
do
        NAME="`basename "$FILE"`"
        if [ -f "folder3/${NAME}" ]
        then
                 echo "not moving ${FILE} since folder2/${NAME} exists"
        else
                 mv -i "${FILE}" "folder2/${NAME}"
        fi
done