-v Adjust (i.e., take the current date and display the result of the adjustment; not actually set
the date) the second, minute, hour, month day, week day, month or year according to val. If
val is preceded with a plus or minus sign, the date is adjusted forwards or backwards according
to the remaining string, otherwise the relevant part of the date is set. The date can be
adjusted as many times as required using these flags. Flags are processed in the order given.
When setting values (rather than adjusting them), seconds are in the range 0-59, minutes are in
the range 0-59, hours are in the range 0-23, month days are in the range 1-31, week days are in
the range 0-6 (Sun-Sat), months are in the range 1-12 (Jan-Dec) and years are in the range
80-38 or 1980-2038.
If val is numeric, one of either y, m, w, d, H, M or S must be used to specify which part of
the date is to be adjusted.
The week day or month may be specified using a name rather than a number. If a name is used
with the plus (or minus) sign, the date will be put forwards (or backwards) to the next (previ-ous) (previous)
ous) date that matches the given week day or month. This will not adjust the date, if the
given week day or month is the same as the current one.
When a date is adjusted to a specific value or in units greater than hours, daylight savings
time considerations are ignored. Adjustments in units of hours or less honor daylight saving
time. So, assuming the current date is March 26, 0:30 and that the DST adjustment means that
the clock goes forward at 01:00 to 02:00, using -v +1H will adjust the date to March 26, 2:30.
Likewise, if the date is October 29, 0:30 and the DST adjustment means that the clock goes back
at 02:00 to 01:00, using -v +3H will be necessary to reach October 29, 2:30.
When the date is adjusted to a specific value that does not actually exist (for example March
26, 1:30 BST 2000 in the Europe/London timezone), the date will be silently adjusted forwards
in units of one hour until it reaches a valid time. When the date is adjusted to a specific
value that occurs twice (for example October 29, 1:30 2000), the resulting timezone will be set
so that the date matches the earlier of the two times.
Adjusting the date by months is inherently ambiguous because a month is a unit of variable
length depending on the current date. This kind of date adjustment is applied in the most
intuitive way. First of all, date tries to preserve the day of the month. If it is impossible
because the target month is shorter than the present one, the last day of the target month will
be the result. For example, using -v +1m on May 31 will adjust the date to June 30, while
using the same option on January 30 will result in the date adjusted to the last day of Febru-ary. February.
ary. This approach is also believed to make the most sense for shell scripting. Nevertheless,
be aware that going forth and back by the same number of months may take you to a different
Refer to the examples below for further details.
An operand with a leading plus (`+') sign signals a user-defined format string which specifies the for-mat format
mat in which to display the date and time. The format string may contain any of the conversion speci-fications specifications
fications described in the strftime(3) manual page, as well as any arbitrary text. A newline (`\n')
character is always output after the characters specified by the format string. The format string for
the default display is ``+%+''.
If an operand does not have a leading plus sign, it is interpreted as a value for setting the system's
notion of the current date and time. The canonical representation for setting the date and time is:
cc Century (either 19 or 20) prepended to the abbreviated year.
yy Year in abbreviated form (e.g., 89 for 1989, 06 for 2006).
mm Numeric month, a number from 1 to 12.
dd Day, a number from 1 to 31.
HH Hour, a number from 0 to 23.
MM Minutes, a number from 0 to 59.
ss Seconds, a number from 0 to 61 (59 plus a maximum of two leap seconds).
Everything but the minutes is optional.
Time changes for Daylight Saving Time, standard time, leap seconds, and leap years are handled automat-ically. automatically.