date(1) says:

STANDARDS
The date utility is expected to be compatible with IEEE Std 1003.2
(“POSIX.2”).

yet the format used for the date string arg is:

[[[[[[CC]yy]mm]dd]HH]MM[.SS]]

whereas POSIX demands

mmddHHMM[[CC]yy]

Why anyone would ever want to use that archaic form is incomprehensible
to me, yet, that is what is required.

Implement support for the POSIX format if POSIXLY_CORRECT is set in
the environment (in the full date(1) build only) in a rather crude
way that relies upon the user getting the format correct.

Tools builds are unaffected - setting the time is not supported there.
(It could be made to work, half setting the time, using -j, is possible
in tools builds, but pointless, and this cheap implementation uses
strptime() which is not necessarily available to a tools build.)

Mention this (very briefly) in the man page.

Add -U and -z options to date(1).

-U allows the (internal) TZ setting to be returned
to what it was when date started running.

-z zone sets TZ to be "zone" unless that is an empty
string, in which case it causes TZ to be removed from
the environment.

These can be used together to manipulate TZ around
parsing of a -d arg, to allow its parsing to be done
in a different zone than the one used for output, and
all unrelated to the initial TZ setting (or system default).

Note that these new options only appear in the first
synopsis form in both the man page and usage(), as -d
also appears only there, and these options make little
sense without also using -d.

This is a very simple change which amounts to no more
that a few setenv() and unsetenv() calls.

Note that the order in which the -u and -d options are given matters.

branches: 1.54.2;
date(1): sync two [[[[[CC]yy]mm]dd]HH]MM[.SS] instances

The markup was the same (modulo Li vs Cm for the dot before the
seconds), but use the same source markup grouping/layout in both to
make this fact more obvious.

date(1): minor markup fixes

Add -R option for displaying time in RFC 5322 format, similar to GNU date.

branches: 1.51.2;
Add -f option to set the time. From FreeBSD.

date(1): Use .Dl for one-liners. Same output is generated.

date(1): Fix the offset in previous.

date(1): add example for how to get seconds since the Epoch output

branches: 1.47.4; 1.47.6;
Remove trailing whitespace and Tn macro.

sync with tzcode-2018c

Remove workaround for ancient HTML generation code.

The range of the SS field is [0,60]

From the POSIX time.h man page:
"The formal definition of UTC does not permit double leap seconds, so all mention of double leap seconds has been removed, and the range shortened from the former [0,61] seconds seen in previous versions of POSIX."

Document the version date first appeared.
Bump date.

branches: 1.42.16;
- fix timed(8) references;
- fix capitalization;
- add reference to environ(7) in `SEE ALSO' section, as it is
mentioned in the text.

From patch by Bug Hunting.

branches: 1.41.6;
Remove trailing whitespace.

For the -d option, refer to parsedate(3) for examples.

Show that "seconds" is the expected argument for -r.
(I didn't bump the manual page date for this minor change. If I
should let me know.)

Drop trailing whitespace.

getdate -> parsedate

Add -d option, similar to gnu date.

Add -j flag to not actually change the clock, just parse the date given
(if any) and then display it in the format given. Matches similar -j
flag functionality in FreeBSD/OpenBSD.

Change requested by George Georgalis on netbsd-users.

While I'm here, disambiguate the letters in the date string, by using
the same option letters as used by strftime(3).

Add a '-a' option to set the time using adjtime(2) instead of settimeofday(2).
Fix usage so that the options which apply to dat/time setting are on the
correct line.

Move UCB-licensed code from 4-clause to 3-clause licence.

Patches provided by Joel Baker in PR 22249, verified by myself.

.Nm does not need a dummy argument ("") before punctuation or
for correct formatting of the SYNOPSIS any longer.

New policy: New sentences start on a new line.
Patches by Robert Elz <kre at munnari oz au>, with minimal changes by me.

Generate <>& symbolically. I'm avoiding .../dist/... directories for now.

Sort sections.

Whitespace nits.

xref settimeofday(2)

Document /etc/localtime, per PR 8099 by Charles Hannum.

Formatting cleanup: more fonts, less punctuation.

branches: 1.24.4;
make example cut&paste-ready

branches: 1.23.2;
Work around a spurious warning.

remove unnecessary comment

Make the documented parsing order for the date match reality.

Fix documentation of `-r'.

Allow a century to be specified.
Cut and paste some text from touch(1) about date parsing.

s/UCT/UTC/

branches: 1.17.2;
Fix .Nm usage.

fix broken timed(8) xrefs, noted by David Brownlee.

Add documentation of the fact that date does indeed understand years
after 2000 (years 00 through 68 are interpreted as meaning 2000-2068;
this should be updated sometime before 2068 :-)

nuke the BUGS section -- it was vax specific

remove obsolete -d and -t options -- kernel timezone handling is long gone

a a => a (close pr 2204).

ENVIRONMENTAL -> ENVIRONMENT

Sync with 4.4lite2

Use "utility" instead of "command". Modern definitions of these terms
are distinct (See POSIX.2 glossary).

A utility is a executable, script or shell builtin; while a command
can be any of those things plus lists, pipelines, compound commands
(if, for, while) and shell function definitions.

convert to new RCS id conventions.

Merge 4.4-Lite version.

Print correct default output format.
Note that date (with a suitable strftime()), is 1003.2 compliant.

1003.2: 4.15.4: The output always shall be terminated by a newline character.

Add RCS indentifiers.

changed "Id" to "Header" for rcsids

added rcs ids to all files

branches: 1.1.1;
Initial revision