What does Linux date -I[TIMESPEC] or –iso-8601[=TIMESPEC] option do?

You can use date -I[FMT] or –iso-8601[=FMT] option to output date/time in ISO 8601 format.  FMT=’date’ for date only (the default), ‘hours’, ‘minutes’, ‘seconds’, or ‘ns’ for date and time to the indicated precision.

date -I[TIMESPEC] or –iso-8601[=TIMESPEC] option example: