coreutils: Calendar date items
1
1 29.2 Calendar date items
1 ========================
1
1 A “calendar date item” specifies a day of the year. It is specified
1 differently, depending on whether the month is specified numerically or
1 literally. All these strings specify the same calendar date:
1
1 1972-09-24 # ISO 8601.
1 72-9-24 # Assume 19xx for 69 through 99,
1 # 20xx for 00 through 68.
1 72-09-24 # Leading zeros are ignored.
1 9/24/72 # Common U.S. writing.
1 24 September 1972
1 24 Sept 72 # September has a special abbreviation.
1 24 Sep 72 # Three-letter abbreviations always allowed.
1 Sep 24, 1972
1 24-sep-72
1 24sep72
1
1 The year can also be omitted. In this case, the last specified year
1 is used, or the current year if none. For example:
1
1 9/24
1 sep 24
1
1 Here are the rules.
1
1 For numeric months, the ISO 8601 format ‘YEAR-MONTH-DAY’ is allowed,
1 where YEAR is any positive number, MONTH is a number between 01 and 12,
1 and DAY is a number between 01 and 31. A leading zero must be present
1 if a number is less than ten. If YEAR is 68 or smaller, then 2000 is
1 added to it; otherwise, if YEAR is less than 100, then 1900 is added to
1 it. The construct ‘MONTH/DAY/YEAR’, popular in the United States, is
1 accepted. Also ‘MONTH/DAY’, omitting the year.
1
1 Literal months may be spelled out in full: ‘January’, ‘February’,
1 ‘March’, ‘April’, ‘May’, ‘June’, ‘July’, ‘August’, ‘September’,
1 ‘October’, ‘November’ or ‘December’. Literal months may be abbreviated
1 to their first three letters, possibly followed by an abbreviating dot.
1 It is also permitted to write ‘Sept’ instead of ‘September’.
1
1 When months are written literally, the calendar date may be given as
1 any of the following:
1
1 DAY MONTH YEAR
1 DAY MONTH
1 MONTH DAY YEAR
1 DAY-MONTH-YEAR
1
1 Or, omitting the year:
1
1 MONTH DAY
1