coreutils: Examples of date
21.1.7 Examples of ‘date’
-------------------------
Here are a few examples. Also see the documentation for the ‘-d’ option
in the previous section.
• 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’.
• To print a date without the leading zero for one-digit days of the
month, you can use the (GNU extension) ‘-’ flag to suppress the
padding altogether:
date -d 1may '+%B %-d'
• To 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
• To set the system clock forward by two minutes:
date --set='+2 minutes'
• To print the date in Internet RFC 5322 format, use ‘date
--rfc-email’. Here is some example output:
Fri, 09 Sep 2005 13:51:39 -0700
• 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 two minutes
after the epoch:
date --date='1970-01-01 00:02:00 +0000' +%s
120
If you do not specify time zone information in the date string,
‘date’ uses your computer’s idea of the time zone when interpreting
the string. For example, if your computer’s time zone is that of
Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
seconds) behind UTC:
# local time zone used
date --date='1970-01-01 00:02:00' +%s
18120
• 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 in Greenwich, England.”
date --date='2000-01-01 UTC' +%s
946684800
An alternative is to use the ‘--utc’ (‘-u’) option. Then you may
omit ‘UTC’ from the date string. Although this produces the same
result for ‘%s’ and many other format sequences, with a time zone
offset different from zero, it would give a different result for
zone-dependent formats like ‘%z’.
date -u --date=2000-01-01 +%s
946684800
To convert such an unwieldy number of seconds back to a more
readable form, use a command like this:
# local time zone used
date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
1999-12-31 19:00:00 -0500
Or if you do not mind depending on the ‘@’ feature present since
coreutils 5.3.0, you could shorten this to:
date -d @946684800 +"%F %T %z"
1999-12-31 19:00:00 -0500
Often it is better to output UTC-relative date and time:
date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
2000-01-01 00:00:00 +0000
• Typically the seconds count omits leap seconds, but some systems
are exceptions. Because leap seconds are not predictable, the
mapping between the seconds count and a future timestamp is not
reliable on the atypical systems that include leap seconds in their
counts.
Here is how the two kinds of systems handle the leap second at
2012-06-30 23:59:60 UTC:
# Typical systems ignore leap seconds:
date --date='2012-06-30 23:59:59 +0000' +%s
1341100799
date --date='2012-06-30 23:59:60 +0000' +%s
date: invalid date '2012-06-30 23:59:60 +0000'
date --date='2012-07-01 00:00:00 +0000' +%s
1341100800
# Atypical systems count leap seconds:
date --date='2012-06-30 23:59:59 +0000' +%s
1341100823
date --date='2012-06-30 23:59:60 +0000' +%s
1341100824
date --date='2012-07-01 00:00:00 +0000' +%s
1341100825