1clock(n) Tcl Built-In Commands clock(n)
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6
8 clock - Obtain and manipulate dates and times
9
11 package require Tcl 8.5
12 clock add timeVal ?count unit...? ?-option value?
14 clock clicks ?-option?
16 clock format timeVal ?-option value...?
18 clock microseconds
20 clock milliseconds
22 clock scan inputString ?-option value...?
24 clock seconds
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28
30 The clock command performs several operations that obtain and manipu‐
31 late values that represent times. The command supports several subcom‐
32 mands that determine what action is carried out by the command.
33 clock add timeVal ?count unit...? ?-option value?
35 Adds a (possibly negative) offset to a time that is expressed as
36 an integer number of seconds. See CLOCK ARITHMETIC for a full
37 description.
38 clock clicks ?-option?
40 If no -option argument is supplied, returns a high-resolution
41 time value as a system-dependent integer value. The unit of the
42 value is system-dependent but should be the highest resolution
43 clock available on the system such as a CPU cycle counter. See
44 HIGH RESOLUTION TIMERS for a full description.
45 If the -option argument is -milliseconds, then the command is
47 synonymous with clock milliseconds (see below). This usage is
48 obsolete, and clock milliseconds is to be considered the pre‐
49 ferred way of obtaining a count of milliseconds.
50 If the -option argument is -microseconds, then the command is
52 synonymous with clock microseconds (see below). This usage is
53 obsolete, and clock microseconds is to be considered the pre‐
54 ferred way of obtaining a count of microseconds.
55 clock format timeVal ?-option value...?
57 Formats a time that is expressed as an integer number of seconds
58 into a format intended for consumption by users or external pro‐
59 grams. See FORMATTING TIMES for a full description.
60 clock microseconds
62 Returns the current time as an integer number of microseconds.
63 See HIGH RESOLUTION TIMERS for a full description.
64 clock milliseconds
66 Returns the current time as an integer number of milliseconds.
67 See HIGH RESOLUTION TIMERS for a full description.
68 clock scan inputString ?-option value...?
70 Scans a time that is expressed as a character string and pro‐
71 duces an integer number of seconds. See SCANNING TIMES for a
72 full description.
73 clock seconds
75 Returns the current time as an integer number of seconds.
76 PARAMETERS
78 count An integer representing a count of some unit of time. See CLOCK
79 ARITHMETIC for the details.
80 timeVal
82 An integer value passed to the clock command that represents an
83 absolute time as a number of seconds from the epoch time of 1
84 January 1970, 00:00 UTC. Note that the count of seconds does
85 not include any leap seconds; seconds are counted as if each UTC
86 day has exactly 86400 seconds. Tcl responds to leap seconds by
87 speeding or slowing its clock by a tiny fraction for some min‐
88 utes until it is back in sync with UTC; its data model does not
89 represent minutes that have 59 or 61 seconds.
90 unit One of the words, seconds, minutes, hours, days, weeks, months,
92 or years, or any unique prefix of such a word. Used in conjunc‐
93 tion with count to identify an interval of time, for example, 3
94 seconds or 1 year.
95 OPTIONS
97 -base time
98 Specifies that any relative times present in a clock scan com‐
99 mand are to be given relative to time. time must be expressed
100 as a count of nominal seconds from the epoch time of 1 January
101 1970, 00:00 UTC.
102 -format format
104 Specifies the desired output format for clock format or the
105 expected input format for clock scan. The format string con‐
106 sists of any number of characters other than the per-cent sign
107 (“%”) interspersed with any number of format groups, which are
108 two-character sequences beginning with the per-cent sign. The
109 permissible format groups, and their interpretation, are
110 described under FORMAT GROUPS.
111 On clock format, the default format is
113 %a %b %d %H:%M:%S %Z %Y
115 On clock scan, the lack of a -format option indicates that a
117 “free format scan” is requested; see FREE FORM SCAN for a
118 description of what happens.
119 -gmt boolean
121 If boolean is true, specifies that a time specified to clock
122 add, clock format or clock scan should be processed in UTC. If
123 boolean is false, the processing defaults to the local time
124 zone. This usage is obsolete; the correct current usage is to
125 specify the UTC time zone with “-timezone :UTC” or any of the
126 equivalent ways to specify it.
127 -locale localeName
129 Specifies that locale-dependent scanning and formatting (and
130 date arithmetic for dates preceding the adoption of the Grego‐
131 rian calendar) is to be done in the locale identified by locale‐
132 Name. The locale name may be any of the locales acceptable to
133 the msgcat package, or it may be the special name system, which
134 represents the current locale of the process, or the null
135 string, which represents Tcl's default locale.
136 The effect of locale on scanning and formatting is discussed in
138 the descriptions of the individual format groups under FORMAT
139 GROUPS. The effect of locale on clock arithmetic is discussed
140 under CLOCK ARITHMETIC.
141 -timezone zoneName
143 Specifies that clock arithmetic, formatting, and scanning are to
144 be done according to the rules for the time zone specified by
145 zoneName. The permissible values, and their interpretation, are
146 discussed under TIME ZONES. On subcommands that expect a -time‐
147 zone argument, the default is to use the current time zone. The
148 current time zone is determined, in order of preference, by:
149 [1] the environment variable TCL_TZ.
151 [2] the environment variable TZ.
153 [3] on Windows systems, the time zone settings from the Con‐
155 trol Panel.
156 If none of these is present, the C localtime and mktime functions are
158 used to attempt to convert times between local and Greenwich. On
159 32-bit systems, this approach is likely to have bugs, particularly for
160 times that lie outside the window (approximately the years 1902 to
161 2037) that can be represented in a 32-bit integer.
162
164 The clock add command performs clock arithmetic on a value (expressed
165 as nominal seconds from the epoch time of 1 January 1970, 00:00 UTC)
166 given as its first argument. The remaining arguments (other than the
167 possible -timezone, -locale and -gmt options) are integers and keywords
168 in alternation, where the keywords are chosen from seconds, minutes,
169 hours, days, weeks, months, or years, or any unique prefix of such a
170 word.
171 Addition of seconds, minutes and hours is fairly straightforward; the
173 given time increment (times sixty for minutes, or 3600 for hours) is
174 simply added to the timeVal given to the clock add command. The result
175 is interpreted as a nominal number of seconds from the Epoch.
176 Surprising results may be obtained when crossing a point at which a
178 leap second is inserted or removed; the clock add command simply
179 ignores leap seconds and therefore assumes that times come in sequence,
180 23:59:58, 23:59:59, 00:00:00. (This assumption is handled by the fact
181 that Tcl's model of time reacts to leap seconds by speeding or slowing
182 the clock by a minuscule amount until Tcl's time is back in step with
183 the world.
184 The fact that adding and subtracting hours is defined in terms of abso‐
186 lute time means that it will add fixed amounts of time in time zones
187 that observe summer time (Daylight Saving Time). For example, the fol‐
188 lowing code sets the value of x to 04:00:00 because the clock has
189 changed in the interval in question.
190 set s [clock scan {2004-10-30 05:00:00} \
192 -format {%Y-%m-%d %H:%M:%S} \
193 -timezone :America/New_York]
194 set a [clock add $s 24 hours -timezone :America/New_York]
195 set x [clock format $a \
196 -format {%H:%M:%S} -timezone :America/New_York]
197 Adding and subtracting days and weeks is accomplished by converting the
199 given time to a calendar day and time of day in the appropriate time
200 zone and locale. The requisite number of days (weeks are converted to
201 days by multiplying by seven) is added to the calendar day, and the
202 date and time are then converted back to a count of seconds from the
203 epoch time.
204 Adding and subtracting a given number of days across the point that the
206 time changes at the start or end of summer time (Daylight Saving Time)
207 results in the same local time on the day in question. For instance,
208 the following code sets the value of x to 05:00:00.
209 set s [clock scan {2004-10-30 05:00:00} \
211 -format {%Y-%m-%d %H:%M:%S} \
212 -timezone :America/New_York]
213 set a [clock add $s 1 day -timezone :America/New_York]
214 set x [clock format $a \
215 -format {%H:%M:%S} -timezone :America/New_York]
216 In cases of ambiguity, where the same local time happens twice on the
218 same day, the earlier time is used. In cases where the conversion
219 yields an impossible time (for instance, 02:30 during the Spring Day‐
220 light Saving Time change using US rules), the time is converted as if
221 the clock had not changed. Thus, the following code will set the value
222 of x to 03:30:00.
223 set s [clock scan {2004-04-03 02:30:00} \
225 -format {%Y-%m-%d %H:%M:%S} \
226 -timezone :America/New_York]
227 set a [clock add $s 1 day -timezone :America/New_York]
228 set x [clock format $a \
229 -format {%H:%M:%S} -timezone :America/New_York]
230 Adding a given number of days or weeks works correctly across the con‐
232 version between the Julian and Gregorian calendars; the omitted days
233 are skipped. The following code sets z to 1752-09-14.
234 set x [clock scan 1752-09-02 -format %Y-%m-%d -locale en_US]
236 set y [clock add $x 1 day -locale en_US]
237 set z [clock format $y -format %Y-%m-%d -locale en_US]
238 In the bizarre case that adding the given number of days yields a date
240 that does not exist because it falls within the dropped days of the
241 Julian-to-Gregorian conversion, the date is converted as if it was on
242 the Julian calendar.
243 Adding a number of months, or a number of years, is similar; it con‐
245 verts the given time to a calendar date and time of day. It then adds
246 the requisite number of months or years, and reconverts the resulting
247 date and time of day to an absolute time.
248 If the resulting date is impossible because the month has too few days
250 (for example, when adding 1 month to 31 January), the last day of the
251 month is substituted. Thus, adding 1 month to 31 January will result
252 in 28 February in a common year or 29 February in a leap year.
253 The rules for handling anomalies relating to summer time and to the
255 Gregorian calendar are the same when adding/subtracting months and
256 years as they are when adding/subtracting days and weeks.
257 If multiple count unit pairs are present on the command, they are eval‐
259 uated consecutively, from left to right.
260
262 Most of the subcommands supported by the clock command deal with times
263 represented as a count of seconds from the epoch time, and this is the
264 representation that clock seconds returns. There are three exceptions,
265 which are all intended for use where higher-resolution times are
266 required. clock milliseconds returns the count of milliseconds from
267 the epoch time, and clock microseconds returns the count of microsec‐
268 onds from the epoch time. In addition, there is a clock clicks command
269 that returns a platform-dependent high-resolution timer. Unlike clock
270 seconds and clock milliseconds, the value of clock clicks is not guar‐
271 anteed to be tied to any fixed epoch; it is simply intended to be the
272 most precise interval timer available, and is intended only for rela‐
273 tive timing studies such as benchmarks.
274
276 The clock format command produces times for display to a user or writ‐
277 ing to an external medium. The command accepts times that are
278 expressed in seconds from the epoch time of 1 January 1970, 00:00 UTC,
279 as returned by clock seconds, clock scan, clock add, file atime or file
280 mtime.
281 If a -format option is present, the following argument is a string that
283 specifies how the date and time are to be formatted. The string con‐
284 sists of any number of characters other than the per-cent sign (“%”)
285 interspersed with any number of format groups, which are two-character
286 sequences beginning with the per-cent sign. The permissible format
287 groups, and their interpretation, are described under FORMAT GROUPS.
288 If a -timezone option is present, the following argument is a string
290 that specifies the time zone in which the date and time are to be for‐
291 matted. As an alternative to “-timezone :UTC”, the obsolete usage
292 “-gmt true” may be used. See TIME ZONES for the permissible variants
293 for the time zone.
294 If a -locale option is present, the following argument is a string that
296 specifies the locale in which the time is to be formatted, in the same
297 format that is used for the msgcat package. Note that the default, if
298 -locale is not specified, is the root locale {} rather than the current
299 locale. The current locale may be obtained by using -locale current.
300 In addition, some platforms support a system locale that reflects the
301 user's current choices. For instance, on Windows, the format that the
302 user has selected from dates and times in the Control Panel can be
303 obtained by using the system locale. On platforms that do not define a
304 user selection of date and time formats separate from LC_TIME, -locale
305 system is synonymous with -locale current.
306
308 The clock scan command accepts times that are formatted as strings and
309 converts them to counts of seconds from the epoch time of 1 January
310 1970, 00:00 UTC. It normally takes a -format option that is followed
311 by a string describing the expected format of the input. (See FREE
312 FORM SCAN for the effect of clock scan without such an argument.) The
313 string consists of any number of characters other than the per-cent
314 sign (“%”), interspersed with any number of format groups, which are
315 two-character sequences beginning with the per-cent sign. The permis‐
316 sible format groups, and their interpretation, are described under FOR‐
317 MAT GROUPS.
318 If a -timezone option is present, the following argument is a string
320 that specifies the time zone in which the date and time are to be
321 interpreted. As an alternative to -timezone :UTC, the obsolete usage
322 -gmt true may be used. See TIME ZONES for the permissible variants for
323 the time zone.
324 If a -locale option is present, the following argument is a string that
326 specifies the locale in which the time is to be interpreted, in the
327 same format that is used for the msgcat package. Note that the
328 default, if -locale is not specified, is the root locale {} rather than
329 the current locale. The current locale may be obtained by using
330 -locale current. In addition, some platforms support a system locale
331 that reflects the user's current choices. For instance, on Windows,
332 the format that the user has selected from dates and times in the Con‐
333 trol Panel can be obtained by using the system locale. On platforms
334 that do not define a user selection of date and time formats separate
335 from LC_TIME, -locale system is synonymous with -locale current.
336 If a -base option is present, the following argument is a time
338 (expressed in seconds from the epoch time) that is used as a base time
339 for interpreting relative times. If no -base option is present, the
340 base time is the current time.
341 Scanning of times in fixed format works by determining three things:
343 the date, the time of day, and the time zone. These three are then
344 combined into a point in time, which is returned as the number of sec‐
345 onds from the epoch.
346 Before scanning begins, the format string is preprocessed to replace
348 %c, %Ec, %x, %Ex, %X. %Ex, %r, %R, %T, %D, %EY and %+ format groups
349 with counterparts that are appropriate to the current locale and con‐
350 tain none of the above groups. For instance, %D will (in the en_US
351 locale) be replaced with %m/%d/%Y.
352 The date is determined according to the fields that are present in the
354 preprocessed format string. In order of preference:
355 [1] If the string contains a %s format group, representing seconds
357 from the epoch, that group is used to determine the date.
358 [2] If the string contains a %J format group, representing the
360 Julian Day Number, that group is used to determine the date.
361 [3] If the string contains a complete set of format groups specify‐
363 ing century, year, month, and day of month; century, year, and
364 day of year; or ISO8601 fiscal year, week of year, and day of
365 week; those groups are combined and used to determine the date.
366 If more than one complete set is present, the one at the right‐
367 most position in the string is used.
368 [4] If the string lacks a century but contains a set of format
370 groups specifying year of century, month and day of month; year
371 of century and day of year; or two-digit ISO8601 fiscal year,
372 week of year, and day of week; those groups are combined and
373 used to determine the date. If more than one complete set is
374 present, the one at the rightmost position in the string is
375 used. The year is presumed to lie in the range 1938 to 2037
376 inclusive.
377 [5] If the string entirely lacks any specification for the year (or
379 contains the year only on the locale's alternative calendar) and
380 contains a set of format groups specifying month and day of
381 month, day of year, or week of year and day of week, those
382 groups are combined and used to determine the date. If more
383 than one complete set is present, the one at the rightmost posi‐
384 tion in the string is used. The year is determined by inter‐
385 preting the base time in the given time zone.
386 [6] If the string contains none of the above sets, but has a day of
388 the month or day of the week, the day of the month or day of the
389 week are used to determine the date by interpreting the base
390 time in the given time zone and returning the given day of the
391 current week or month. (The week runs from Monday to Sunday,
392 ISO8601-fashion.) If both day of month and day of week are
393 present, the day of the month takes priority.
394 [7] If none of the above rules results in a usable date, the date of
396 the base time in the given time zone is used.
397 The time is also determined according to the fields that are present in
399 the preprocessed format string. In order of preference:
400 [1] If the string contains a %s format group, representing seconds
402 from the epoch, that group determines the time of day.
403 [2] If the string contains either an hour on the 24-hour clock or an
405 hour on the 12-hour clock plus an AM/PM indicator, that hour
406 determines the hour of the day. If the string further contains
407 a group specifying the minute of the hour, that group combines
408 with the hour. If the string further contains a group specify‐
409 ing the second of the minute, that group combines with the hour
410 and minute.
411 [3] If the string contains neither a %s format group nor a group
413 specifying the hour of the day, then midnight (00:00, the start
414 of the given date) is used. The time zone is determined by
415 either the -timezone or -gmt options, or by using the current
416 time zone.
417 If a format string lacks a %z or %Z format group, it is possible for
419 the time to be ambiguous because it appears twice in the same day, once
420 without and once with Daylight Saving Time. If this situation occurs,
421 the first occurrence of the time is chosen. (For this reason, it is
422 wise to have the input string contain the time zone when converting
423 local times. This caveat does not apply to UTC times.)
424
426 The following format groups are recognized by the clock scan and clock
427 format commands.
428 %a On output, receives an abbreviation (e.g., Mon) for the day of
430 the week in the given locale. On input, matches the name of the
431 day of the week in the given locale (in either abbreviated or
432 full form, or any unique prefix of either form).
433 %A On output, receives the full name (e.g., Monday) of the day of
435 the week in the given locale. On input, matches the name of the
436 day of the week in the given locale (in either abbreviated or
437 full form, or any unique prefix of either form).
438 %b On output, receives an abbreviation (e.g., Jan) for the name of
440 the month in the given locale. On input, matches the name of
441 the month in the given locale (in either abbreviated or full
442 form, or any unique prefix of either form).
443 %B On output, receives the full name (e.g., January) of the month
445 in the given locale. On input, matches the name of the month in
446 the given locale (in either abbreviated or full form, or any
447 unique prefix of either form).
448 %c On output, receives a localized representation of date and time
450 of day; the localized representation is expected to use the Gre‐
451 gorian calendar. On input, matches whatever %c produces.
452 %C On output, receives the number of the century in Indo-Arabic
454 numerals. On input, matches one or two digits, possibly with
455 leading whitespace, that are expected to be the number of the
456 century.
457 %d On output, produces the number of the day of the month, as two
459 decimal digits. On input, matches one or two digits, possibly
460 with leading whitespace, that are expected to be the number of
461 the day of the month.
462 %D This format group is synonymous with %m/%d/%Y. It should be
464 used only in exchanging data within the en_US locale, since
465 other locales typically do not use this order for the fields of
466 the date.
467 %e On output, produces the number of the day of the month, as one
469 or two decimal digits (with a leading blank for one-digit
470 dates). On input, matches one or two digits, possibly with
471 leading whitespace, that are expected to be the number of the
472 day of the month.
473 %Ec On output, produces a locale-dependent representation of the
475 date and time of day in the locale's alternative calendar. On
476 input, matches whatever %Ec produces. The locale's alternative
477 calendar need not be the Gregorian calendar.
478 %EC On output, produces a locale-dependent name of an era in the
480 locale's alternative calendar. On input, matches the name of
481 the era or any unique prefix.
482 %EE On output, produces the string B.C.E. or C.E., or a string of
484 the same meaning in the locale, to indicate whether %Y refers to
485 years before or after Year 1 of the Common Era. On input,
486 accepts the string B.C.E., B.C., C.E., A.D., or the abbreviation
487 appropriate to the current locale, and uses it to fix whether %Y
488 refers to years before or after Year 1 of the Common Era.
489 %Ex On output, produces a locale-dependent representation of the
491 date in the locale's alternative calendar. On input, matches
492 whatever %Ex produces. The locale's alternative calendar need
493 not be the Gregorian calendar.
494 %EX On output, produces a locale-dependent representation of the
496 time of day in the locale's alternative numerals. On input,
497 matches whatever %EX produces.
498 %Ey On output, produces a locale-dependent number of the year of the
500 era in the locale's alternative calendar and numerals. On
501 input, matches such a number.
502 %EY On output, produces a representation of the year in the locale's
504 alternative calendar and numerals. On input, matches what %EY
505 produces. Often synonymous with %EC%Ey.
506 %g On output, produces a two-digit year number suitable for use
508 with the week-based ISO8601 calendar; that is, the year number
509 corresponds to the week number produced by %V. On input,
510 accepts such a two-digit year number, possibly with leading
511 whitespace.
512 %G On output, produces a four-digit year number suitable for use
514 with the week-based ISO8601 calendar; that is, the year number
515 corresponds to the week number produced by %V. On input,
516 accepts such a four-digit year number, possibly with leading
517 whitespace.
518 %h This format group is synonymous with %b.
520 %H On output, produces a two-digit number giving the hour of the
522 day (00-23) on a 24-hour clock. On input, accepts such a num‐
523 ber.
524 %I On output, produces a two-digit number giving the hour of the
526 day (12-11) on a 12-hour clock. On input, accepts such a num‐
527 ber.
528 %j On output, produces a three-digit number giving the day of the
530 year (001-366). On input, accepts such a number.
531 %J On output, produces a string of digits giving the Julian Day
533 Number. On input, accepts a string of digits and interprets it
534 as a Julian Day Number. The Julian Day Number is a count of the
535 number of calendar days that have elapsed since 1 January, 4713
536 BCE of the proleptic Julian calendar. The epoch time of 1 Janu‐
537 ary 1970 corresponds to Julian Day Number 2440588.
538 %k On output, produces a one- or two-digit number giving the hour
540 of the day (0-23) on a 24-hour clock. On input, accepts such a
541 number.
542 %l On output, produces a one- or two-digit number giving the hour
544 of the day (12-11) on a 12-hour clock. On input, accepts such a
545 number.
546 %m On output, produces the number of the month (01-12) with exactly
548 two digits. On input, accepts two digits and interprets them as
549 the number of the month.
550 %M On output, produces the number of the minute of the hour (00-59)
552 with exactly two digits. On input, accepts two digits and
553 interprets them as the number of the minute of the hour.
554 %N On output, produces the number of the month (1-12) with one or
556 two digits, and a leading blank for one-digit dates. On input,
557 accepts one or two digits, possibly with leading whitespace, and
558 interprets them as the number of the month.
559 %Od, %Oe, %OH, %OI, %Ok, %Ol, %Om, %OM, %OS, %Ou, %Ow, %Oy
561 All of these format groups are synonymous with their counter‐
562 parts without the “O”, except that the string is produced and
563 parsed in the locale-dependent alternative numerals.
564 %p On output, produces an indicator for the part of the day, AM or
566 PM, appropriate to the given locale. If the script of the given
567 locale supports multiple letterforms, lowercase is preferred.
568 On input, matches the representation AM or PM in the given
569 locale, in either case.
570 %P On output, produces an indicator for the part of the day, am or
572 pm, appropriate to the given locale. If the script of the given
573 locale supports multiple letterforms, uppercase is preferred.
574 On input, matches the representation AM or PM in the given
575 locale, in either case.
576 %Q This format group is reserved for internal use within the Tcl
578 library.
579 %r On output, produces a locale-dependent time of day representa‐
581 tion on a 12-hour clock. On input, accepts whatever %r produces.
582 %R On output, the time in 24-hour notation (%H:%M). For a version
584 including the seconds, see %T below. On input, accepts whatever
585 %R produces.
586 %s On output, simply formats the timeVal argument as a decimal
588 integer and inserts it into the output string. On input,
589 accepts a decimal integer and uses is as the time value without
590 any further processing. Since %s uniquely determines a point in
591 time, it overrides all other input formats.
592 %S On output, produces a two-digit number of the second of the
594 minute (00-59). On input, accepts two digits and uses them as
595 the second of the minute.
596 %t On output, produces a TAB character. On input, matches a TAB
598 character.
599 %T Synonymous with %H:%M:%S.
601 %u On output, produces the number of the day of the week (1→Monday,
603 7→Sunday). On input, accepts a single digit and interprets it as
604 the day of the week. Sunday may be either 0 or 7.
605 %U On output, produces the ordinal number of the week of the year
607 (00-53). The first Sunday of the year is the first day of week
608 01. On input accepts two digits which are otherwise ignored.
609 This format group is never used in determining an input date.
610 This interpretation of the week of the year was once common in
611 US banking but is now largely obsolete. See %V for the ISO8601
612 week number.
613 %V On output, produces the number of the ISO8601 week as a two
615 digit number (01-53). Week 01 is the week containing January 4;
616 or the first week of the year containing at least 4 days; or the
617 week containing the first Thursday of the year (the three state‐
618 ments are equivalent). Each week begins on a Monday. On input,
619 accepts the ISO8601 week number.
620 %w On output, produces the ordinal number of the day of the week
622 (Sunday==0; Saturday==6). On input, accepts a single digit and
623 interprets it as the day of the week; Sunday may be represented
624 as either 0 or 7. Note that %w is not the ISO8601 weekday num‐
625 ber, which is produced and accepted by %u.
626 %W On output, produces a week number (00-53) within the year; week
628 01 begins on the first Monday of the year. On input, accepts two
629 digits, which are otherwise ignored. This format group is never
630 used in determining an input date. It is not the ISO8601 week
631 number; that week is produced and accepted by %V.
632 %x On output, produces the date in a locale-dependent representa‐
634 tion. On input, accepts whatever %x produces and is used to
635 determine calendar date.
636 %X On output, produces the time of day in a locale-dependent repre‐
638 sentation. On input, accepts whatever %X produces and is used to
639 determine time of day.
640 %y On output, produces the two-digit year of the century. On input,
642 accepts two digits, and is used to determine calendar date. The
643 date is presumed to lie between 1938 and 2037 inclusive. Note
644 that %y does not yield a year appropriate for use with the
645 ISO8601 week number %V; programs should use %g for that purpose.
646 %Y On output, produces the four-digit calendar year. On input,
648 accepts four digits and may be used to determine calendar date.
649 Note that %Y does not yield a year appropriate for use with the
650 ISO8601 week number %V; programs should use %G for that purpose.
651 %z On output, produces the current time zone, expressed in hours
653 and minutes east (+hhmm) or west (-hhmm) of Greenwich. On input,
654 accepts a time zone specifier (see TIME ZONES below) that will
655 be used to determine the time zone.
656 %Z On output, produces the current time zone's name, possibly
658 translated to the given locale. On input, accepts a time zone
659 specifier (see TIME ZONES below) that will be used to determine
660 the time zone. This option should, in general, be used on input
661 only when parsing RFC822 dates. Other uses are fraught with
662 ambiguity; for instance, the string BST may represent British
663 Summer Time or Brazilian Standard Time. It is recommended that
664 date/time strings for use by computers use numeric time zones
665 instead.
666 %% On output, produces a literal “%” character. On input, matches a
668 literal “%” character.
669 %+ Synonymous with “%a %b %e %H:%M:%S %Z %Y”.
671
673 When the clock command is processing a local time, it has several pos‐
674 sible sources for the time zone to use. In order of preference, they
675 are:
676 [1] A time zone specified inside a string being parsed and matched
678 by a %z or %Z format group.
679 [2] A time zone specified with the -timezone option to the clock
681 command (or, equivalently, by -gmt 1).
682 [3] A time zone specified in an environment variable TCL_TZ.
684 [4] A time zone specified in an environment variable TZ.
686 [5] The local time zone from the Control Panel on Windows systems.
688 [6] The C library's idea of the local time zone, as defined by the
690 mktime and localtime functions.
691 In case [1] only, the string is tested to see if it is one of the
693 strings:
694 gmt ut utc bst wet wat at
696 nft nst ndt ast adt est edt
697 cst cdt mst mdt pst pdt yst
698 ydt hst hdt cat ahst nt idlw
699 cet cest met mewt mest swt sst
700 eet eest bt it zp4 zp5 ist
701 zp6 wast wadt jt cct jst cast
702 cadt east eadt gst nzt nzst nzdt
703 idle
704 If it is a string in the above list, it designates a known time zone,
706 and is interpreted as such.
707 For time zones in case [1] that do not match any of the above strings,
709 and always for cases [2]-[6], the following rules apply.
710 If the time zone begins with a colon, it is one of a standardized list
712 of names like :America/New_York that give the rules for various
713 locales. A complete list of the location names is too lengthy to be
714 listed here. On most Tcl installations, the definitions of the loca‐
715 tions are to be found in named files in the directory
716 “/no_backup/tools/lib/tcl8.5/clock/tzdata”. On some Unix systems,
717 these files are omitted, and the definitions are instead obtained from
718 system files in “/usr/share/zoneinfo”, “/usr/share/lib/zoneinfo” or
719 “/usr/local/etc/zoneinfo”. As a special case, the name :localtime
720 refers to the local time zone as defined by the C library.
721 A time zone string consisting of a plus or minus sign followed by four
723 or six decimal digits is interpreted as an offset in hours, minutes,
724 and seconds (if six digits are present) from UTC. The plus sign
725 denotes a sign east of Greenwich; the minus sign one west of Greenwich.
726 A time zone string conforming to the Posix specification of the TZ
728 environment variable will be recognized. The specification may be
729 found at http://www.open‐
730 group.org/onlinepubs/009695399/basedefs/xbd_chap08.html.
731 If the Posix time zone string contains a DST (Daylight Savings Time)
733 part, but doesn't contain a rule stating when DST starts or ends, then
734 default rules are used. For Timezones with an offset between 0 and +12,
735 the current European/Russian rules are used, otherwise the current US
736 rules are used. In Europe (offset +0 to +2) the switch to summertime is
737 done each last Sunday in March at 1:00 GMT, and the switch back is each
738 last Sunday in October at 2:00 GMT. In Russia (offset +3 to +12), the
739 switch dates are the same, only the switch to summertime is at 2:00
740 local time, and the switch back is at 3:00 local time in all time
741 zones. The US switch to summertime takes place each second Sunday in
742 March at 2:00 local time, and the switch back is each first Sunday in
743 November at 3:00 local time. These default rules mean that in all Euro‐
744 pean, Russian and US (or compatible) time zones, DST calculations will
745 be correct for dates in 2007 and later, unless in the future the rules
746 change again.
747 Any other time zone string is processed by prefixing a colon and
749 attempting to use it as a location name, as above.
750
752 Developers wishing to localize the date and time formatting and parsing
753 are referred to http://tip.tcl.tk/173 for a specification.
754
756 If the clock scan command is invoked without a -format option, then it
757 requests a free-form scan. This form of scan is deprecated. The rea‐
758 son for the deprecation is that there are too many ambiguities. (Does
759 the string “2000” represent a year, a time of day, or a quantity?) No
760 set of rules for interpreting free-form dates and times has been found
761 to give unsurprising results in all cases.
762 If free-form scan is used, only the -base and -gmt options are
764 accepted. The -timezone and -locale options will result in an error if
765 -format is not supplied.
766 For the benefit of users who need to understand legacy code that uses
768 free-form scan, the documentation for how free-form scan interprets a
769 string is included here:
770 If only a time is specified, the current date is assumed. If the
772 inputString does not contain a time zone mnemonic, the local time zone
773 is assumed, unless the -gmt argument is true, in which case the clock
774 value is calculated assuming that the specified time is relative to
775 Greenwich Mean Time. -gmt, if specified, affects only the computed
776 time value; it does not impact the interpretation of -base.
777 If the -base flag is specified, the next argument should contain an
779 integer clock value. Only the date in this value is used, not the
780 time. This is useful for determining the time on a specific day or
781 doing other date-relative conversions.
782 The inputString argument consists of zero or more specifications of the
784 following form:
785 time A time of day, which is of the form: hh?:mm?:ss?? ?meridian?
787 ?zone? or hhmm ?meridian? ?zone? If no meridian is specified,
788 hh is interpreted on a 24-hour clock.
789 date A specific month and day with optional year. The acceptable
791 formats are “mm/dd?/yy?”, “monthname dd?, yy?”, “day, dd month‐
792 name ?yy?”, “dd monthname yy”, “?CC?yymmdd”, and “dd-month‐
793 name-?CC?yy”. The default year is the current year. If the
794 year is less than 100, we treat the years 00-68 as 2000-2068 and
795 the years 69-99 as 1969-1999. Not all platforms can represent
796 the years 38-70, so an error may result if these years are used.
797 ISO 8601 point-in-time
799 An ISO 8601 point-in-time specification, such as “CCyymmddThh‐
800 mmss,” where T is the literal “T”, “CCyymmdd hhmmss”, or “CCyym‐
801 mddThh:mm:ss”. Note that only these three formats are accepted.
802 The command does not accept the full range of point-in-time
803 specifications specified in ISO8601. Other formats can be rec‐
804 ognized by giving an explicit -format option to the clock scan
805 command.
806 relative time
808 A specification relative to the current time. The format is
809 number unit. Acceptable units are year, fortnight, month, week,
810 day, hour, minute (or min), and second (or sec). The unit can
811 be specified as a singular or plural, as in 3 weeks. These mod‐
812 ifiers may also be specified: tomorrow, yesterday, today, now,
813 last, this, next, ago.
814 The actual date is calculated according to the following steps.
816 First, any absolute date and/or time is processed and converted. Using
818 that time as the base, day-of-week specifications are added. Next,
819 relative specifications are used. If a date or day is specified, and
820 no absolute or relative time is given, midnight is used. Finally, a
821 correction is applied so that the correct hour of the day is produced
822 after allowing for daylight savings time differences and the correct
823 date is given when going from the end of a long month to a short month.
824
826 msgcat(n)
827
829 clock, date, time
830
832 Copyright (c) 2004 Kevin B. Kenny <kennykb@acm.org>. All rights
833 reserved.
834Tcl 8.5 clock(n)