Some GREP_OPTIONS will modify the output of the grep commands that are looking for the assembly jars in bin/spark-class.
For example, if the -n option is specified, the grep output will look like:
This will not match the regular expressions, and so the jar files will not be found. We could improve the regular expression to handle cases like this and trim off extra characters, but it is difficult to know which options may or may not be set. Unsetting GREP_OPTIONS within the script handles all the cases and gives the desired output.
By the way, the actual error seen from the commandline was this: