If an extension is not installed, then
grass72 /geo/grassdb/global/mdt_wgs84/PERMANENT/ --exec i.landsat8.swlst
Cleaning up temporary files...
Starting GRASS GIS...
Executing <i.landsat8.swlst> ...
should report that the extension is not installed, instead of
ERROR: Execution of <i.landsat8.swlst> failed:
[Errno 2] No such file or directory
Exiting...
which can/does make a user think there is missing/potentially faulty input file,
subject to an extension's parameter.
Makes sense?
Thank you, Nikos