Fixed issue file type detection (shell script vs.
not work on some Linux platforms, due to slightly different output
from 'file' on shell scripts on different platforms. Type
detection logic is now more robust.
The test suite will catch this when we add support for
Rocky Linux 8.
Also corrected a copy/paste error in an error message and
enhanced code comments.
This is a bug fix to a new, not-yet-released feature.