File: coreutils.info, Node: date invocation, Next: arch invocation, Up: System context 21.1 'date': Print or set system date and time ============================================== Synopses: date [OPTION]... [+FORMAT] date [-u|--utc|--universal] [ MMDDhhmm[[CC]YY][.ss] ] Invoking 'date' with no FORMAT argument is equivalent to invoking it with a default format that depends on the 'LC_TIME' locale category. In the default C locale, this format is ''+%a %b %e %H:%M:%S %Z %Y'', so the output looks like 'Thu Mar 3 13:47:51 PST 2005'. Normally, 'date' uses the time zone rules indicated by the 'TZ' environment variable, or the system default rules if 'TZ' is not set. *Note Specifying the Time Zone with 'TZ': (libc)TZ Variable. If given an argument that starts with a '+', 'date' prints the current date and time (or the date and time specified by the '--date' option, see below) in the format defined by that argument, which is similar to that of the 'strftime' function. Except for conversion specifiers, which start with '%', characters in the format string are printed unchanged. The conversion specifiers are described below. An exit status of zero indicates success, and a nonzero value indicates failure. * Menu: * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ] * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY] * Literal conversion specifiers:: %[%nt] * Padding and other flags:: Pad with zeros, spaces, etc. * Setting the time:: Changing the system clock. * Options for date:: Instead of the current time. * Date input formats:: Specifying date strings. * Examples of date:: Examples. File: coreutils.info, Node: Time conversion specifiers, Next: Date conversion specifiers, Up: date invocation 21.1.1 Time conversion specifiers --------------------------------- 'date' conversion specifiers related to times. '%H' hour ('00'...'23') '%I' hour ('01'...'12') '%k' hour, space padded (' 0'...'23'); equivalent to '%_H'. This is a GNU extension. '%l' hour, space padded (' 1'...'12'); equivalent to '%_I'. This is a GNU extension. '%M' minute ('00'...'59') '%N' nanoseconds ('000000000'...'999999999'). This is a GNU extension. '%p' locale's equivalent of either 'AM' or 'PM'; blank in many locales. Noon is treated as 'PM' and midnight as 'AM'. '%P' like '%p', except lower case. This is a GNU extension. '%r' locale's 12-hour clock time (e.g., '11:11:04 PM') '%R' 24-hour hour and minute. Same as '%H:%M'. '%s' seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC. Leap seconds are not counted unless leap second support is available. *Note %s-examples::, for examples. This is a GNU extension. '%S' second ('00'...'60'). This may be '60' if leap seconds are supported. '%T' 24-hour hour, minute, and second. Same as '%H:%M:%S'. '%X' locale's time representation (e.g., '23:13:48') '%z' Four-digit numeric time zone, e.g., '-0600' or '+0530', or '-0000' if no time zone is determinable. This value reflects the numeric time zone appropriate for the current time, using the time zone rules specified by the 'TZ' environment variable. A time zone is not determinable if its numeric offset is zero and its abbreviation begins with '-'. The time (and optionally, the time zone rules) can be overridden by the '--date' option. '%:z' Numeric time zone with ':', e.g., '-06:00' or '+05:30'), or '-00:00' if no time zone is determinable. This is a GNU extension. '%::z' Numeric time zone to the nearest second with ':' (e.g., '-06:00:00' or '+05:30:00'), or '-00:00:00' if no time zone is determinable. This is a GNU extension. '%:::z' Numeric time zone with ':' using the minimum necessary precision (e.g., '-06', '+05:30', or '-04:56:02'), or '-00' if no time zone is determinable. This is a GNU extension. '%Z' alphabetic time zone abbreviation (e.g., 'EDT'), or nothing if no time zone is determinable. See '%z' for how it is determined. File: coreutils.info, Node: Date conversion specifiers, Next: Literal conversion specifiers, Prev: Time conversion specifiers, Up: date invocation 21.1.2 Date conversion specifiers --------------------------------- 'date' conversion specifiers related to dates. '%a' locale's abbreviated weekday name (e.g., 'Sun') '%A' locale's full weekday name, variable length (e.g., 'Sunday') '%b' locale's abbreviated month name (e.g., 'Jan') '%B' locale's full month name, variable length (e.g., 'January') '%c' locale's date and time (e.g., 'Thu Mar 3 23:05:25 2005') '%C' century. This is like '%Y', except the last two digits are omitted. For example, it is '20' if '%Y' is '2000', and is '-0' if '%Y' is '-001'. It is normally at least two characters, but it may be more. '%d' day of month (e.g., '01') '%D' date; same as '%m/%d/%y' '%e' day of month, space padded; same as '%_d' '%F' full date in ISO 8601 format; like '%+4Y-%m-%d' except that any flags or field width override the '+' and (after subtracting 6) the '4'. This is a good choice for a date format, as it is standard and is easy to sort in the usual case where years are in the range 0000...9999. '%g' year corresponding to the ISO week number, but without the century (range '00' through '99'). This has the same format and value as '%y', except that if the ISO week number (see '%V') belongs to the previous or next year, that year is used instead. '%G' year corresponding to the ISO week number. This has the same format and value as '%Y', except that if the ISO week number (see '%V') belongs to the previous or next year, that year is used instead. It is normally useful only if '%V' is also used; for example, the format '%G-%m-%d' is probably a mistake, since it combines the ISO week number year with the conventional month and day. '%h' same as '%b' '%j' day of year ('001'...'366') '%m' month ('01'...'12') '%q' quarter of year ('1'...'4') '%u' day of week ('1'...'7') with '1' corresponding to Monday '%U' week number of year, with Sunday as the first day of the week ('00'...'53'). Days in a new year preceding the first Sunday are in week zero. '%V' ISO week number, that is, the week number of year, with Monday as the first day of the week ('01'...'53'). If the week containing January 1 has four or more days in the new year, then it is considered week 1; otherwise, it is week 53 of the previous year, and the next week is week 1. (See the ISO 8601 standard.) '%w' day of week ('0'...'6') with 0 corresponding to Sunday '%W' week number of year, with Monday as first day of week ('00'...'53'). Days in a new year preceding the first Monday are in week zero. '%x' locale's date representation (e.g., '12/31/99') '%y' last two digits of year ('00'...'99') '%Y' year. This is normally at least four characters, but it may be more. Year '0000' precedes year '0001', and year '-001' precedes year '0000'. File: coreutils.info, Node: Literal conversion specifiers, Next: Padding and other flags, Prev: Date conversion specifiers, Up: date invocation 21.1.3 Literal conversion specifiers ------------------------------------ 'date' conversion specifiers that produce literal strings. '%%' a literal % '%n' a newline '%t' a horizontal tab File: coreutils.info, Node: Padding and other flags, Next: Setting the time, Prev: Literal conversion specifiers, Up: date invocation 21.1.4 Padding and other flags ------------------------------ Unless otherwise specified, 'date' normally pads numeric fields with zeros, so that, for example, numeric months are always output as two digits. Seconds since the epoch are not padded, though, since there is no natural width for them. The following optional flags can appear after the '%': '-' (hyphen) Do not pad the field; useful if the output is intended for human consumption. This is a GNU extension. '_' (underscore) Pad with spaces; useful if you need a fixed number of characters in the output, but zeros are too distracting. This is a GNU extension. '0' (zero) Pad with zeros even if the conversion specifier would normally pad with spaces. '+' Pad with zeros, like '0'. In addition, precede any year number with '+' if it exceeds 9999 or if its field width exceeds 4; similarly, precede any century number with '+' if it exceeds 99 or if its field width exceeds 2. This supports ISO 8601 formats for dates far in the future; for example, the command 'date --date=12019-02-25 +%+13F' outputs the string '+012019-02-25'. '^' Use upper case characters if possible. This is a GNU extension. '#' Use opposite case characters if possible. A field that is normally upper case becomes lower case, and vice versa. This is a GNU extension. Here are some examples of padding: date +%d/%m -d "Feb 1" => 01/02 date +%-d/%-m -d "Feb 1" => 1/2 date +%_d/%_m -d "Feb 1" => 1/ 2 You can optionally specify the field width (after any flag, if present) as a decimal number. If the natural size of the output of the field has less than the specified number of characters, the result is written right adjusted and padded to the given size. For example, '%9B' prints the right adjusted month name in a field of width 9. An optional modifier can follow the optional flag and width specification. The modifiers are: 'E' Use the locale's alternate representation for date and time. This modifier applies to the '%c', '%C', '%x', '%X', '%y' and '%Y' conversion specifiers. In a Japanese locale, for example, '%Ex' might yield a date format based on the Japanese Emperors' reigns. 'O' Use the locale's alternate numeric symbols for numbers. This modifier applies only to numeric conversion specifiers. If the format supports the modifier but no alternate representation is available, it is ignored. POSIX specifies the behavior of flags and field widths only for '%C', '%F', '%G', and '%Y' (all without modifiers), and requires a flag to be present if and only if a field width is also present. Other combinations of flags, field widths and modifiers are GNU extensions. File: coreutils.info, Node: Setting the time, Next: Options for date, Prev: Padding and other flags, Up: date invocation 21.1.5 Setting the time ----------------------- If given an argument that does not start with '+', 'date' sets the system clock to the date and time specified by that argument (as described below). You must have appropriate privileges to set the system clock. Note for changes to persist across a reboot, the hardware clock may need to be updated from the system clock, which might not happen automatically on your system. The argument must consist entirely of digits, which have the following meaning: 'MM' month 'DD' day within month 'hh' hour 'mm' minute 'CC' first two digits of year (optional) 'YY' last two digits of year (optional) 'ss' second (optional) Note, the '--date' and '--set' options may not be used with an argument in the above format. The '--universal' option may be used with such an argument to indicate that the specified date and time are relative to Universal Time rather than to the local time zone. File: coreutils.info, Node: Options for date, Next: Examples of date, Prev: Setting the time, Up: date invocation 21.1.6 Options for 'date' ------------------------- The program accepts the following options. Also see *note Common options::. '-d DATESTR' '--date=DATESTR' Display the date and time specified in DATESTR instead of the current date and time. DATESTR can be in almost any common format. It can contain month names, time zones, 'am' and 'pm', 'yesterday', etc. For example, '--date="2004-02-27 14:19:13.489392193 +0530"' specifies the instant of time that is 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30 minutes east of UTC. Note: input currently must be in locale independent format. E.g., the LC_TIME=C below is needed to print back the correct date in many locales: date -d "$(LC_TIME=C date)" *Note Date input formats::. '--debug' Annotate the parsed date, display the effective time zone, and warn about potential misuse. '-f DATEFILE' '--file=DATEFILE' Parse each line in DATEFILE as with '-d' and display the resulting date and time. If DATEFILE is '-', use standard input. This is useful when you have many dates to process, because the system overhead of starting up the 'date' executable many times can be considerable. '-I[TIMESPEC]' '--iso-8601[=TIMESPEC]' Display the date using an ISO 8601 format, '%Y-%m-%d'. The argument TIMESPEC specifies the number of additional terms of the time to include. It can be one of the following: 'auto' Print just the date. This is the default if TIMESPEC is omitted. 'hours' Append the hour of the day to the date. 'minutes' Append the hours and minutes. 'seconds' Append the hours, minutes and seconds. 'ns' Append the hours, minutes, seconds and nanoseconds. If showing any time terms, then include the time zone using the format '%:z'. This format is always suitable as input for the '--date' ('-d') and '--file' ('-f') options, regardless of the current locale. '-r FILE' '--reference=FILE' Display the date and time of the last modification of FILE, instead of the current date and time. '-R' '--rfc-email' Display the date and time using the format '%a, %d %b %Y %H:%M:%S %z', evaluated in the C locale so abbreviations are always in English. For example: Fri, 09 Sep 2005 13:51:39 -0700 This format conforms to Internet RFCs 5322 (https://tools.ietf.org/search/rfc5322), 2822 (https://tools.ietf.org/search/rfc2822) and 822 (https://tools.ietf.org/search/rfc822), the current and previous standards for Internet email. For compatibility with older versions of 'date', '--rfc-2822' and '--rfc-822' are aliases for '--rfc-email'. '--rfc-3339=TIMESPEC' Display the date using a format specified by Internet RFC 3339 (https://tools.ietf.org/search/rfc3339). This is like '--iso-8601', except that a space rather than a 'T' separates dates from times. This format is always suitable as input for the '--date' ('-d') and '--file' ('-f') options, regardless of the current locale. The argument TIMESPEC specifies how much of the time to include. It can be one of the following: 'date' Print just the full-date, e.g., '2005-09-14'. This is equivalent to the format '%Y-%m-%d'. 'seconds' Print the full-date and full-time separated by a space, e.g., '2005-09-14 00:56:06+05:30'. The output ends with a numeric time-offset; here the '+05:30' means that local time is five hours and thirty minutes east of UTC. This is equivalent to the format '%Y-%m-%d %H:%M:%S%:z'. 'ns' Like 'seconds', but also print nanoseconds, e.g., '2005-09-14 00:56:06.998458565+05:30'. This is equivalent to the format '%Y-%m-%d %H:%M:%S.%N%:z'. '-s DATESTR' '--set=DATESTR' Set the date and time to DATESTR. See '-d' above. See also *note Setting the time::. '-u' '--utc' '--universal' Use Universal Time by operating as if the 'TZ' environment variable were set to the string 'UTC0'. UTC stands for Coordinated Universal Time, established in 1960. Universal Time is often called "Greenwich Mean Time" (GMT) for historical reasons. Typically, systems ignore leap seconds and thus implement an approximation to UTC rather than true UTC. File: coreutils.info, Node: Date input formats, Next: Version sort ordering, Prev: File timestamps, Up: Top 29 Date input formats ********************* First, a quote: Our units of temporal measurement, from seconds on up to months, are so complicated, asymmetrical and disjunctive so as to make coherent mental reckoning in time all but impossible. Indeed, had some tyrannical god contrived to enslave our minds to time, to make it all but impossible for us to escape subjection to sodden routines and unpleasant surprises, he could hardly have done better than handing down our present system. It is like a set of trapezoidal building blocks, with no vertical or horizontal surfaces, like a language in which the simplest thought demands ornate constructions, useless particles and lengthy circumlocutions. Unlike the more successful patterns of language and science, which enable us to face experience boldly or at least level-headedly, our system of temporal calculation silently and persistently encourages our terror of time. ... It is as though architects had to measure length in feet, width in meters and height in ells; as though basic instruction manuals demanded a knowledge of five different languages. It is no wonder then that we often look into our own immediate past or future, last Tuesday or a week from Sunday, with feelings of helpless confusion. ... --Robert Grudin, 'Time and the Art of Living'. This section describes the textual date representations that GNU programs accept. These are the strings you, as a user, can supply as arguments to the various programs. The C interface (via the 'parse_datetime' function) is not described here. * Menu: * General date syntax:: Common rules. * Calendar date items:: 19 Dec 1994. * Time of day items:: 9:20pm. * Time zone items:: EST, PDT, UTC, ... * Combined date and time of day items:: 1972-09-24T20:02:00,000000-0500. * Day of week items:: Monday and others. * Relative items in date strings:: next tuesday, 2 years ago. * Pure numbers in date strings:: 19931219, 1440. * Seconds since the Epoch:: @1078100502. * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0". * Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al. File: coreutils.info, Node: General date syntax, Next: Calendar date items, Up: Date input formats 29.1 General date syntax ======================== A "date" is a string, possibly empty, containing many items separated by whitespace. The whitespace may be omitted when no ambiguity arises. The empty string means the beginning of today (i.e., midnight). Order of the items is immaterial. A date string may contain many flavors of items: * calendar date items * time of day items * time zone items * combined date and time of day items * day of the week items * relative items * pure numbers. We describe each of these item types in turn, below. A few ordinal numbers may be written out in words in some contexts. This is most useful for specifying day of the week items or relative items (see below). Among the most commonly used ordinal numbers, the word 'last' stands for -1, 'this' stands for 0, and 'first' and 'next' both stand for 1. Because the word 'second' stands for the unit of time there is no way to write the ordinal number 2, but for convenience 'third' stands for 3, 'fourth' for 4, 'fifth' for 5, 'sixth' for 6, 'seventh' for 7, 'eighth' for 8, 'ninth' for 9, 'tenth' for 10, 'eleventh' for 11 and 'twelfth' for 12. When a month is written this way, it is still considered to be written numerically, instead of being "spelled in full"; this changes the allowed strings. In the current implementation, only English is supported for words and abbreviations like 'AM', 'DST', 'EST', 'first', 'January', 'Sunday', 'tomorrow', and 'year'. The output of the 'date' command is not always acceptable as a date string, not only because of the language problem, but also because there is no standard meaning for time zone items like 'IST'. When using 'date' to generate a date string intended to be parsed later, specify a date format that is independent of language and that does not use time zone items other than 'UTC' and 'Z'. Here are some ways to do this: $ LC_ALL=C TZ=UTC0 date Mon Mar 1 00:21:42 UTC 2004 $ TZ=UTC0 date +'%Y-%m-%d %H:%M:%SZ' 2004-03-01 00:21:42Z $ date --rfc-3339=ns # --rfc-3339 is a GNU extension. 2004-02-29 16:21:42.692722128-08:00 $ date --rfc-2822 # a GNU extension Sun, 29 Feb 2004 16:21:42 -0800 $ date +'%Y-%m-%d %H:%M:%S %z' # %z is a GNU extension. 2004-02-29 16:21:42 -0800 $ date +'@%s.%N' # %s and %N are GNU extensions. @1078100502.692722128 Alphabetic case is completely ignored in dates. Comments may be introduced between round parentheses, as long as included parentheses are properly nested. Hyphens not followed by a digit are currently ignored. Leading zeros on numbers are ignored. Invalid dates like '2005-02-29' or times like '24:00' are rejected. In the typical case of a host that does not support leap seconds, a time like '23:59:60' is rejected even if it corresponds to a valid leap second. File: coreutils.info, Node: Calendar date items, Next: Time of day items, Prev: General date syntax, Up: Date input formats 29.2 Calendar date items ======================== A "calendar date item" specifies a day of the year. It is specified differently, depending on whether the month is specified numerically or literally. All these strings specify the same calendar date: 1972-09-24 # ISO 8601. 72-9-24 # Assume 19xx for 69 through 99, # 20xx for 00 through 68. 72-09-24 # Leading zeros are ignored. 9/24/72 # Common U.S. writing. 24 September 1972 24 Sept 72 # September has a special abbreviation. 24 Sep 72 # Three-letter abbreviations always allowed. Sep 24, 1972 24-sep-72 24sep72 The year can also be omitted. In this case, the last specified year is used, or the current year if none. For example: 9/24 sep 24 Here are the rules. For numeric months, the ISO 8601 format 'YEAR-MONTH-DAY' is allowed, where YEAR is any positive number, MONTH is a number between 01 and 12, and DAY is a number between 01 and 31. A leading zero must be present if a number is less than ten. If YEAR is 68 or smaller, then 2000 is added to it; otherwise, if YEAR is less than 100, then 1900 is added to it. The construct 'MONTH/DAY/YEAR', popular in the United States, is accepted. Also 'MONTH/DAY', omitting the year. Literal months may be spelled out in full: 'January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November' or 'December'. Literal months may be abbreviated to their first three letters, possibly followed by an abbreviating dot. It is also permitted to write 'Sept' instead of 'September'. When months are written literally, the calendar date may be given as any of the following: DAY MONTH YEAR DAY MONTH MONTH DAY YEAR DAY-MONTH-YEAR Or, omitting the year: MONTH DAY File: coreutils.info, Node: Time of day items, Next: Time zone items, Prev: Calendar date items, Up: Date input formats 29.3 Time of day items ====================== A "time of day item" in date strings specifies the time on a given day. Here are some examples, all of which represent the same time: 20:02:00.000000 20:02 8:02pm 20:02-0500 # In EST (U.S. Eastern Standard Time). More generally, the time of day may be given as 'HOUR:MINUTE:SECOND', where HOUR is a number between 0 and 23, MINUTE is a number between 0 and 59, and SECOND is a number between 0 and 59 possibly followed by '.' or ',' and a fraction containing one or more digits. Alternatively, ':SECOND' can be omitted, in which case it is taken to be zero. On the rare hosts that support leap seconds, SECOND may be 60. If the time is followed by 'am' or 'pm' (or 'a.m.' or 'p.m.'), HOUR is restricted to run from 1 to 12, and ':MINUTE' may be omitted (taken to be zero). 'am' indicates the first half of the day, 'pm' indicates the second half of the day. In this notation, 12 is the predecessor of 1: midnight is '12am' while noon is '12pm'. (This is the zero-oriented interpretation of '12am' and '12pm', as opposed to the old tradition derived from Latin which uses '12m' for noon and '12pm' for midnight.) The time may alternatively be followed by a time zone correction, expressed as 'SHHMM', where S is '+' or '-', HH is a number of zone hours and MM is a number of zone minutes. The zone minutes term, MM, may be omitted, in which case the one- or two-digit correction is interpreted as a number of hours. You can also separate HH from MM with a colon. When a time zone correction is given this way, it forces interpretation of the time relative to Coordinated Universal Time (UTC), overriding any previous specification for the time zone or the local time zone. For example, '+0530' and '+05:30' both stand for the time zone 5.5 hours ahead of UTC (e.g., India). This is the best way to specify a time zone correction by fractional parts of an hour. The maximum zone correction is 24 hours. Either 'am'/'pm' or a time zone correction may be specified, but not both. File: coreutils.info, Node: Time zone items, Next: Combined date and time of day items, Prev: Time of day items, Up: Date input formats 29.4 Time zone items ==================== A "time zone item" specifies an international time zone, indicated by a small set of letters, e.g., 'UTC' or 'Z' for Coordinated Universal Time. Any included periods are ignored. By following a non-daylight-saving time zone by the string 'DST' in a separate word (that is, separated by some white space), the corresponding daylight saving time zone may be specified. Alternatively, a non-daylight-saving time zone can be followed by a time zone correction, to add the two values. This is normally done only for 'UTC'; for example, 'UTC+05:30' is equivalent to '+05:30'. Time zone items other than 'UTC' and 'Z' are obsolescent and are not recommended, because they are ambiguous; for example, 'EST' has a different meaning in Australia than in the United States, and 'A' has different meaning as a military time zone than as an obsolescent RFC 822 time zone. Instead, it's better to use unambiguous numeric time zone corrections like '-0500', as described in the previous section. If neither a time zone item nor a time zone correction is supplied, timestamps are interpreted using the rules of the default time zone (*note Specifying time zone rules::). File: coreutils.info, Node: Combined date and time of day items, Next: Day of week items, Prev: Time zone items, Up: Date input formats 29.5 Combined date and time of day items ======================================== The ISO 8601 date and time of day extended format consists of an ISO 8601 date, a 'T' character separator, and an ISO 8601 time of day. This format is also recognized if the 'T' is replaced by a space. In this format, the time of day should use 24-hour notation. Fractional seconds are allowed, with either comma or period preceding the fraction. ISO 8601 fractional minutes and hours are not supported. Typically, hosts support nanosecond timestamp resolution; excess precision is silently discarded. Here are some examples: 2012-09-24T20:02:00.052-05:00 2012-12-31T23:59:59,999999999+11:00 1970-01-01 00:00Z File: coreutils.info, Node: Day of week items, Next: Relative items in date strings, Prev: Combined date and time of day items, Up: Date input formats 29.6 Day of week items ====================== The explicit mention of a day of the week will forward the date (only if necessary) to reach that day of the week in the future. Days of the week may be spelled out in full: 'Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday' or 'Saturday'. Days may be abbreviated to their first three letters, optionally followed by a period. The special abbreviations 'Tues' for 'Tuesday', 'Wednes' for 'Wednesday' and 'Thur' or 'Thurs' for 'Thursday' are also allowed. A number may precede a day of the week item to move forward supplementary weeks. It is best used in expression like 'third monday'. In this context, 'last DAY' or 'next DAY' is also acceptable; they move one week before or after the day that DAY by itself would represent. A comma following a day of the week item is ignored. File: coreutils.info, Node: Relative items in date strings, Next: Pure numbers in date strings, Prev: Day of week items, Up: Date input formats 29.7 Relative items in date strings =================================== "Relative items" adjust a date (or the current date if none) forward or backward. The effects of relative items accumulate. Here are some examples: 1 year 1 year ago 3 years 2 days The unit of time displacement may be selected by the string 'year' or 'month' for moving by whole years or months. These are fuzzy units, as years and months are not all of equal duration. More precise units are 'fortnight' which is worth 14 days, 'week' worth 7 days, 'day' worth 24 hours, 'hour' worth 60 minutes, 'minute' or 'min' worth 60 seconds, and 'second' or 'sec' worth one second. An 's' suffix on these units is accepted and ignored. The unit of time may be preceded by a multiplier, given as an optionally signed number. Unsigned numbers are taken as positively signed. No number at all implies 1 for a multiplier. Following a relative item by the string 'ago' is equivalent to preceding the unit by a multiplier with value -1. The string 'tomorrow' is worth one day in the future (equivalent to 'day'), the string 'yesterday' is worth one day in the past (equivalent to 'day ago'). The strings 'now' or 'today' are relative items corresponding to zero-valued time displacement, these strings come from the fact a zero-valued time displacement represents the current time when not otherwise changed by previous items. They may be used to stress other items, like in '12:00 today'. The string 'this' also has the meaning of a zero-valued time displacement, but is preferred in date strings like 'this thursday'. When a relative item causes the resulting date to cross a boundary where the clocks were adjusted, typically for daylight saving time, the resulting date and time are adjusted accordingly. The fuzz in units can cause problems with relative items. For example, '2003-07-31 -1 month' might evaluate to 2003-07-01, because 2003-06-31 is an invalid date. To determine the previous month more reliably, you can ask for the month before the 15th of the current month. For example: $ date -R Thu, 31 Jul 2003 13:02:39 -0700 $ date --date='-1 month' +'Last month was %B?' Last month was July? $ date --date="$(date +%Y-%m-15) -1 month" +'Last month was %B!' Last month was June! Also, take care when manipulating dates around clock changes such as daylight saving leaps. In a few cases these have added or subtracted as much as 24 hours from the clock, so it is often wise to adopt universal time by setting the 'TZ' environment variable to 'UTC0' before embarking on calendrical calculations. File: coreutils.info, Node: Pure numbers in date strings, Next: Seconds since the Epoch, Prev: Relative items in date strings, Up: Date input formats 29.8 Pure numbers in date strings ================================= The precise interpretation of a pure decimal number depends on the context in the date string. If the decimal number is of the form YYYYMMDD and no other calendar date item (*note Calendar date items::) appears before it in the date string, then YYYY is read as the year, MM as the month number and DD as the day of the month, for the specified calendar date. If the decimal number is of the form HHMM and no other time of day item appears before it in the date string, then HH is read as the hour of the day and MM as the minute of the hour, for the specified time of day. MM can also be omitted. If both a calendar date and a time of day appear to the left of a number in the date string, but no relative item, then the number overrides the year. File: coreutils.info, Node: Seconds since the Epoch, Next: Specifying time zone rules, Prev: Pure numbers in date strings, Up: Date input formats 29.9 Seconds since the Epoch ============================ If you precede a number with '@', it represents an internal timestamp as a count of seconds. The number can contain an internal decimal point (either '.' or ','); any excess precision not supported by the internal representation is truncated toward minus infinity. Such a number cannot be combined with any other date item, as it specifies a complete timestamp. Internally, computer times are represented as a count of seconds since an epoch--a well-defined point of time. On GNU and POSIX systems, the epoch is 1970-01-01 00:00:00 UTC, so '@0' represents this time, '@1' represents 1970-01-01 00:00:01 UTC, and so forth. GNU and most other POSIX-compliant systems support such times as an extension to POSIX, using negative counts, so that '@-1' represents 1969-12-31 23:59:59 UTC. Traditional Unix systems count seconds with 32-bit two's-complement integers and can represent times from 1901-12-13 20:45:52 through 2038-01-19 03:14:07 UTC. More modern systems use 64-bit counts of seconds with nanosecond subcounts, and can represent all the times in the known lifetime of the universe to a resolution of 1 nanosecond. On most hosts, these counts ignore the presence of leap seconds. For example, on most hosts '@915148799' represents 1998-12-31 23:59:59 UTC, '@915148800' represents 1999-01-01 00:00:00 UTC, and there is no way to represent the intervening leap second 1998-12-31 23:59:60 UTC. File: coreutils.info, Node: Specifying time zone rules, Next: Authors of parse_datetime, Prev: Seconds since the Epoch, Up: Date input formats 29.10 Specifying time zone rules ================================ Normally, dates are interpreted using the rules of the current time zone, which in turn are specified by the 'TZ' environment variable, or by a system default if 'TZ' is not set. To specify a different set of default time zone rules that apply just to one date, start the date with a string of the form 'TZ="RULE"'. The two quote characters ('"') must be present in the date, and any quotes or backslashes within RULE must be escaped by a backslash. For example, with the GNU 'date' command you can answer the question "What time is it in New York when a Paris clock shows 6:30am on October 31, 2004?" by using a date beginning with 'TZ="Europe/Paris"' as shown in the following shell transcript: $ export TZ="America/New_York" $ date --date='TZ="Europe/Paris" 2004-10-31 06:30' Sun Oct 31 01:30:00 EDT 2004 In this example, the '--date' operand begins with its own 'TZ' setting, so the rest of that operand is processed according to 'Europe/Paris' rules, treating the string '2004-10-31 06:30' as if it were in Paris. However, since the output of the 'date' command is processed according to the overall time zone rules, it uses New York time. (Paris was normally six hours ahead of New York in 2004, but this example refers to a brief Halloween period when the gap was five hours.) A 'TZ' value is a rule that typically names a location in the 'tz' database (https://www.iana.org/time-zones). A recent catalog of location names appears in the TWiki Date and Time Gateway (https://twiki.org/cgi-bin/xtra/tzdatepick.html). A few non-GNU hosts require a colon before a location name in a 'TZ' setting, e.g., 'TZ=":America/New_York"'. The 'tz' database includes a wide variety of locations ranging from 'Arctic/Longyearbyen' to 'Antarctica/South_Pole', but if you are at sea and have your own private time zone, or if you are using a non-GNU host that does not support the 'tz' database, you may need to use a POSIX rule instead. Simple POSIX rules like 'UTC0' specify a time zone without daylight saving time; other rules can specify simple daylight saving regimes. *Note Specifying the Time Zone with 'TZ': (libc)TZ Variable. File: coreutils.info, Node: Authors of parse_datetime, Prev: Specifying time zone rules, Up: Date input formats 29.11 Authors of 'parse_datetime' ================================= 'parse_datetime' started life as 'getdate', as originally implemented by Steven M. Bellovin (<smb AT research.com>) while at the University of North Carolina at Chapel Hill. The code was later tweaked by a couple of people on Usenet, then completely overhauled by Rich $alz (<rsalz AT bbn.com>) and Jim Berets (<jberets AT bbn.com>) in August, 1990. Various revisions for the GNU system were made by David MacKenzie, Jim Meyering, Paul Eggert and others, including renaming it to 'get_date' to avoid a conflict with the alternative Posix function 'getdate', and a later rename to 'parse_datetime'. The Posix function 'getdate' can parse more locale-specific dates using 'strptime', but relies on an environment variable and external file, and lacks the thread-safety of 'parse_datetime'. This chapter was originally produced by Franc,ois Pinard (<pinard AT iro.ca>) from the 'parse_datetime.y' source code, and then edited by K. Berry (<kb AT cs.edu>). File: coreutils.info, Node: Examples of date, Prev: Options for date, Up: date invocation 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
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