Examples of `date'

* To print the date of the day before yesterday:
date --date='2 days ago'

* To print the date of the day three months and one day hence:
date --date='3 months 1 day'

* To print the day of year of Christmas in the current year:
date --date='25 Dec' +%j

* To print the current full month name and the day of the month:
date '+%B %d'

But this may not be what you want because for the first nine days
of the month, the `%d' expands to a zero-padded two-digit field,
for example `date -d 1may '+%B %d'' will print `May 01'.

* Print a date without the leading zero for one-digit days of the
month, you can use the (GNU extension) `-' modifier to suppress
the padding altogether.
date -d=1may '+%B %-d'

* Print the current date and time in the format required by many
non-GNU versions of `date' when setting the system clock:
date +%m%d%H%M%Y.%S

* Set the system date and time
date --set="2002-6-29 11:59 AM"

* Set the system clock forward by two minutes:
date --set='+2 minutes'

* Print the date in the format specified by RFC-822, use `date
--rfc'. I just did and saw this:

Mon, 25 Mar 1996 23:34:17 -0600

* To convert a date string to the number of seconds since the epoch
(which is 1970-01-01 00:00:00 UTC), use the `--date' option with
the `%s' format. That can be useful in sorting and/or graphing
and/or comparing data by date. The following command outputs the
number of the seconds since the epoch for the time one second later
than the epoch, but in time zone five hours later (Cambridge,
Massachusetts), thus a total of five hours and one second after
the epoch:

date --date='1970-01-01 00:00:01 UTC +5 hours' +%s
18001

Suppose you had _not_ specified time zone information in the
example above. Then, date would have used your computer's idea of
the time zone when interpreting the string. Here's what you would
get if you were in Greenwich, England:

# local time zone used
date --date='1970-01-01 00:00:01' +%s
1

* If you're sorting or graphing dated data, your raw date values may
be represented as seconds since the epoch. But few people can
look at the date `946684800' and casually note "Oh, that's the
first second of the year 2000."

date --date='2000-01-01 UTC' +%s
946684800

To convert such an unwieldy number of seconds back to a more
readable form, use a command like this:

date -d '1970-01-01 946684800 sec' +"%Y-%m-%d %T %z"
2000-01-01 00:00:00 +0000