Correct error message to be consistent with the current location of the output/temp dirs - they are not necessarily subdirectories of the input dir anymore.
Add TODO: We assume that grep expects UTF-8 input. This might not be true for systems which have a different default charset. I found no way to specify the charset which grep uses for its input, so this TODO is about documenting that the script might not work on non UTF-8 systems.
Properly terminate "case" branch