ISO8601
$ man date
-I[TIMESPEC], --iso-8601[=TIMESPEC]
output date/time in ISO 8601 format. TIMESPEC='date' for date only (the default), 'hours', 'minutes', 'seconds', or 'ns' for date and time to
the indicated precision.
$ date --iso-8601
2023-01-22
$ date --iso-8601=date
2023-01-22
$ date --iso-8601=hours
2023-01-22T14+0900
$ date --iso-8601=minutes
2023-01-22T14:01+0900
$ date --iso-8601=seconds
2023-01-22T14:01:16+0900
$ date --iso-8601=ns
2023-01-22T14:01:16,631109694+0900
RFC2822/RFC3339
-R, --rfc-2822
output date and time in RFC 2822 format. Example: Mon, 07 Aug 2006 12:34:56 -0600
--rfc-3339=TIMESPEC
output date and time in RFC 3339 format. TIMESPEC='date', 'seconds', or 'ns' for date and time to the indicated precision. Date and time com-
ponents are separated by a single space: 2006-08-07 12:34:56-06:00
--- date command output with RFC 2822 format ---
$ date --rfc-2822
Sun, 22 Jan 2023 14:12:25 +0900
--- date command output with RFC 3399 format ---
$ date --rfc-3339=date
2023-01-22
$ date --rfc-3339=seconds
2023-01-22 14:12:25+09:00
$ date --rfc-3339=ns
2023-01-22 14:12:25.698220571+09:00