我添加了spark bin目录的路径，但是当我执行spark-shell时，它没有运行。
# pwd
/usr/local/spark/bin
# echo $PATH
/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/spark/bin
# spark-shell
spark-shell is not found, please check if spark is installed
/usr/bin/spark-shell: line 26: exec: : not found
我做错了什么？