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clock(n)			      Tcl Built-In Commands				 clock(n)


       clock - Obtain and manipulate time

       clock option ?arg arg ...?

       This  command  performs one of several operations that may obtain or manipulate strings or
       values that represent some notion of time.  The option argument determines what action  is
       carried out by the command.  The legal options (which may be abbreviated) are:

       clock clicks ?-milliseconds?								  |
	      Return  a high-resolution time value as a system-dependent integer value.  The unit |
	      of the value is system-dependent but should be the highest resolution clock  avail- |
	      able on the system such as a CPU cycle counter. If -milliseconds is specified, then |
	      the value is guaranteed to be of millisecond granularity.  This value  should  only |
	      be used for the relative measurement of elapsed time.

       clock format clockValue ?-format string? ?-gmt boolean?
	      Converts an integer time value, typically returned by clock seconds, clock scan, or
	      the atime, mtime, or ctime options of the file command, to human-readable form.  If
	      the  -format  argument  is present the next argument is a string that describes how
	      the date and time are to be formatted.  Field descriptors consist of a  %  followed
	      by  a field descriptor character.  All other characters are copied into the result.
	      Valid field descriptors are:

	      %%     Insert a %.

	      %a     Abbreviated weekday name (Mon, Tue, etc.).

	      %A     Full weekday name (Monday, Tuesday, etc.).

	      %b     Abbreviated month name (Jan, Feb, etc.).

	      %B     Full month name.

	      %c     Locale specific date and time.

	      %d     Day of month (01 - 31).

	      %H     Hour in 24-hour format (00 - 23).

	      %I     Hour in 12-hour format (00 - 12).

	      %j     Day of year (001 - 366).

	      %m     Month number (01 - 12).

	      %M     Minute (00 - 59).

	      %p     AM/PM indicator.

	      %S     Seconds (00 - 59).

	      %U     Week of year (00 - 52), Sunday is the first day of the week.

	      %w     Weekday number (Sunday = 0).

	      %W     Week of year (00 - 52), Monday is the first day of the week.

	      %x     Locale specific date format.

	      %X     Locale specific time format.

	      %y     Year without century (00 - 99).

	      %Y     Year with century (e.g. 1990)

	      %Z     Time zone name.

	      In addition, the following field descriptors may be supported on some systems (e.g.
	      Unix but not Windows):

	      %D     Date as %m/%d/%y.

	      %e     Day of month (1 - 31), no leading zeros.

	      %h     Abbreviated month name.

	      %n     Insert a newline.

	      %r     Time as %I:%M:%S %p.

	      %R     Time as %H:%M.

	      %t     Insert a tab.

	      %T     Time as %H:%M:%S.

	      If  the  -format argument is not specified, the format string "%a %b %d %H:%M:%S %Z
	      %Y" is used.  If the -gmt argument is present the next argument must be  a  boolean
	      which  if true specifies that the time will be formatted as Greenwich Mean Time. If
	      false then the local timezone will be used as defined by the operating environment.

       clock scan dateString ?-base clockVal? ?-gmt boolean?
	      Convert dateString to an integer clock value (see clock seconds).  This command can
	      parse and convert virtually any standard date and/or time string, which can include
	      standard time zone mnemonics.  If only a time is specified,  the	current  date  is
	      assumed.	 If the string does not contain a time zone mnemonic, the local time zone
	      is assumed, unless the -gmt argument is true, in which case the clock value is cal-
	      culated assuming that the specified time is relative to Greenwich Mean Time.  -gmt,
	      if specified, affects only the computed time value; it does not impact  the  inter-
	      pretation of -base.

	      If  the  -base flag is specified, the next argument should contain an integer clock
	      value.  Only the date in this value is used, not the  time.   This  is  useful  for
	      determining the time on a specific day or doing other date-relative conversions.

	      The dateString consists of zero or more specifications of the following form:

	      time   A time of day, which is of the form: hh?:mm?:ss??	?meridian? ?zone? or hhmm
		     ?meridian?  ?zone?. If no meridian is specified,  hh  is  interpreted  on	a
		     24-hour clock.

	      date   A	specific  month  and  day with optional year.  The acceptable formats are
		     mm/dd?/yy?, monthname dd ?, yy?, dd monthname ?yy?, day,  dd  monthname  yy,
		     ?CC?yymmdd, ?CC?yy-mm-dd, dd-monthname-?CC?yy.  The default year is the cur-
		     rent year.  If the year is less than  100,  we  treat  the  years	00-68  as |
		     2000-2068 and the years 69-99 as 1969-1999.  Not all platforms can represent |
		     the years 38-70, so an error may result if these years are used.

	      ISO 8601 point-in-time
		     An ISO 8601 point-in-time specification, such as CCyymmddThhmmss, where T is
		     the literal T, CCyymmdd hhmmss, or CCyymmddThh:mm:ss.

	      relative time
		     A	specification  relative  to  the current time.	The format is number unit
		     acceptable units are year, fortnight, month, week,  day,  hour,  minute  (or
		     min),  and second (or sec).  The unit can be specified as a singular or plu-
		     ral, as in 3 weeks.  These modifiers may also be specified:  tomorrow,  yes-
		     terday, today, now, last, this, next, ago.

	      The  actual  date is calculated according to the following steps.  First, any abso-
	      lute date and/or time is processed and converted.  Using that  time  as  the  base,
	      day-of-week  specifications are added.  Next, relative specifications are used.  If
	      a date or day is specified, and no absolute or relative time is given, midnight  is
	      used.  Finally, a correction is applied so that the correct hour of the day is pro-
	      duced after allowing for daylight savings time differences and the correct date  is
	      given when going from the end of a long month to a short month.

	      Daylight	savings  time correction is applied only when the relative time is speci-
	      fied in units of days or more, ie, days, weeks, fortnights, months or years.   This
	      means that when crossing the daylight savings time boundary, different results will
	      be given for clock scan "1 day" and clock scan "24 hours":
		     % clock scan "1 day" -base [clock scan 1999-10-31]
		     % clock scan "24 hours" -base [clock scan 1999-10-31]

       clock seconds
	      Return the current date and time as a system-dependent integer value.  The unit  of
	      the  value  is seconds, allowing it to be used for relative time calculations.  The
	      value is usually defined as total elapsed time from an  ``epoch''.   You	shouldn't
	      assume the value of the epoch.

       clock, date, time

Tcl					       8.3					 clock(n)
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