mknod error while trying to make a device driver file with shell
The most likely cause of this error is that $major has no value. That is, $major is blank.
You have the echo statement there: what does it show? If you don't see anything, you might want to enhance it to show nothing enlightenlingly;
echo "major='$major'"which will produce something like
major='213'if all is well, and show empty quotes if it is working like I suspect.