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       zshcalsys - zsh calendar system


       The  shell  is  supplied with a series of functions to replace and enhance the traditional
       Unix calendar programme, which warns the user of imminent or  future  events,  details  of
       which  are  stored  in a text file (typically calendar in the user's home directory).  The
       version provided here includes a mechanism for alerting the user when an event is due.

       In addition a function age is provided that can be used in a  glob  qualifier;  it  allows
       files to be selected based on their modification times.

       The  format  of  the calendar file and the dates used there in and in the age function are
       described first, then the functions that can be called to examine and modify the  calendar

       The  functions here depend on the availability of the zsh/datetime module which is usually
       installed with the shell.  The library  function  strptime()  must  be  available;  it  is
       present on most recent operating systems.


   Calendar File Format
       The  calendar  file is by default ~/calendar.  This can be configured by the calendar-file
       style, see the section STYLES below.  The basic format consists of a  series  of  separate
       lines,  with  no  indentation,  each including a date and time specification followed by a
       description of the event.

       Various enhancements to this format are supported, based on the syntax of  Emacs  calendar
       mode.   An  indented  line indicates a continuation line that continues the description of
       the event from the preceding line (note the date may not be continued in  this  way).   An
       initial ampersand (&) is ignored for compatibility.

       An  indented  line  on which the first non-whitespace character is # is not displayed with
       the calendar entry, but is still scanned for  information.   This  can  be  used  to  hide
       information  useful  to  the  calendar  system  but  not  to  the user, such as the unique
       identifier used by calendar_add.

       The Emacs extension that a date with no description may refer to a  number  of  succeeding
       events at different times is not supported.

       Unless  the  done-file  style  has  been altered, any events which have been processed are
       appended to the file with the same name as the calendar file with the suffix .done,  hence
       ~/calendar.done by default.

       An example is shown below.

   Date Format
       The  format  of  the  date  and  time  is  designed to allow flexibility without admitting
       ambiguity.  (The words `date' and `time' are both used in the documentation below;  except
       where  specifically  noted  this  implies a string that may include both a date and a time
       specification.)  Note that there is no localization support; month and day names  must  be
       in English and separator characters are fixed.  Matching is case insensitive, and only the
       first three letters of the names are significant,  although  as  a  special  case  a  form
       beginning  "month"  does not match "Monday".  Furthermore, time zones are not handled; all
       times are assumed to be local.

       It is recommended that, rather than exploring the intricacies of the system, users find  a
       date  format that is natural to them and stick to it.  This will avoid unexpected effects.
       Various key facts should be noted.

       ·      In particular, note the confusion between month/day/year  and  day/month/year  when
              the  month  is  numeric;  these formats should be avoided if at all possible.  Many
              alternatives are available.

       ·      The year must be given in full to avoid confusion, and only years from 1900 to 2099
              inclusive are matched.

       The  following  give  some obvious examples; users finding here a format they like and not
       subject to vagaries of style may skip the  full  description.   As  dates  and  times  are
       matched separately (even though the time may be embedded in the date), any date format may
       be mixed with any format for the time of day provide the separators are clear (whitespace,
       colons, commas).

              2007/04/03 13:13
              2007/04/03 1:13 pm
              3rd April 2007, 13:13
              April 3rd 2007 1:13 p.m.
              Apr 3, 2007 13:13
              Tue Apr 03 13:13:00 2007
              13:13 2007/apr/3

       More detailed rules follow.

       Times  are  parsed and extracted before dates.  They must use colons to separate hours and
       minutes, though a dot is allowed before seconds if they are  present.   This  limits  time
       formats to the following:

       ·      HH:MM[:SS[.FFFFF]] [am|pm|a.m.|p.m.]

       ·      HH:MM.SS[.FFFFF] [am|pm|a.m.|p.m.]

       Here,  square  brackets indicate optional elements, possibly with alternatives.  Fractions
       of a second are recognised but ignored.  For absolute times (the normal format require  by
       the  calendar file and the age function) a date is mandatory but a time of day is not; the
       time returned is at the start of the date.  One variation is allowed: if a.m. or  p.m.  or
       one of their variants is present, an hour without a minute is allowed, e.g. 3 p.m..

       Time  zones  are  not  handled, though if one is matched following a time specification it
       will be removed to allow a surrounding date to be parsed.  This only happens if the format
       of  the  timezone  is  not  too  unusual.   The  following  are examples of forms that are


       Any part of the timezone that is not numeric must have exactly three  capital  letters  in
       the name.

       Dates suffer from the ambiguity between DD/MM/YYYY and MM/DD/YYYY.  It is recommended this
       form is avoided with purely numeric dates, but use  of  ordinals,  eg.  3rd/04/2007,  will
       resolve the ambiguity as the ordinal is always parsed as the day of the month.  Years must
       be four digits (and the first two must be 19 or 20); 03/04/08 is  not  recognised.   Other
       numbers may have leading zeroes, but they are not required.  The following are handled:

       ·      YYYY/MM/DD

       ·      YYYY-MM-DD

       ·      YYYY/MNM/DD

       ·      YYYY-MNM-DD

       ·      DD[th|st|rd] MNM[,] [ YYYY ]

       ·      MNM DD[th|st|rd][,] [ YYYY ]

       ·      DD[th|st|rd]/MM[,] YYYY

       ·      DD[th|st|rd]/MM/YYYY

       ·      MM/DD[th|st|rd][,] YYYY

       ·      MM/DD[th|st|rd]/YYYY

       Here, MNM is at least the first three letters of a month name, matched case-insensitively.
       The remainder of the month name may appear but its contents are irrelevant, so  janissary,
       febrile, martial, apricot, maybe, junta, etc. are happily handled.

       Where the year is shown as optional, the current year is assumed.  There are only two such
       cases, the form Jun 20 or 14 September (the only two commonly occurring forms, apart  from
       a  "the"  in  some forms of English, which isn't currently supported).  Such dates will of
       course become ambiguous in the future, so should ideally be avoided.

       Times may follow dates with a colon, e.g. 1965/07/12:09:45; this is in order to provide  a
       format  with  no  whitespace.  A comma and whitespace are allowed, e.g. 1965/07/12, 09:45.
       Currently the order of these separators is not  checked,  so  illogical  formats  such  as
       1965/07/12,  :  ,09:45 will also be matched.  For simplicity such variations are not shown
       in the list above.  Otherwise, a time is only recognised as being associated with  a  date
       if there is only whitespace in between, or if the time was embedded in the date.

       Days  of the week are not normally scanned, but will be ignored if they occur at the start
       of the date pattern only.  However, in contexts  where  it  is  useful  to  specify  dates
       relative  to  today,  days of the week with no other date specification may be given.  The
       day is assumed to be either today or within the past week.  Likewise, the words yesterday,
       today  and  tomorrow  are  handled.   All matches are case-insensitive.  Hence if today is
       Monday, then Sunday is equivalent to yesterday, Monday is equivalent to today, but Tuesday
       gives  a date six days ago.  This is not generally useful within the calendar file.  Dates
       in this format may be combined with a time specification; for example Tomorrow, 8 p.m..

       For example, the standard date format:

              Fri Aug 18 17:00:48 BST 2006

       is handled by matching HH:MM:SS and removing it together with  the  matched  (but  unused)
       time zone.  This leaves the following:

              Fri Aug 18 2006

       Fri is ignored and the rest is matched according to the standard rules.

   Relative Time Format
       In  certain  places  relative  times  are handled.  Here, a date is not allowed; instead a
       combination of various supported periods are allowed, together with an optional time.  The
       periods must be in order from most to least significant.

       In  some  cases,  a  more  accurate  calculation is possible when there is an anchor date:
       offsets of months or years pick the correct day, rather than  being  rounded,  and  it  is
       possible to pick a particular day in a month as `(1st Friday)', etc., as described in more
       detail below.

       Anchors are available in the following cases.  If one or  two  times  are  passed  to  the
       function  calendar,  the  start  time acts an anchor for the end time when the end time is
       relative (even if the start  time  is  implicit).   When  examining  calendar  files,  the
       scheduled  event  being  examined  anchors the warning time when it is given explicitly by
       means of the WARN keyword; likewise, the scheduled event anchors a repetition period  when
       given  by  the  RPT keyword, so that specifications such as RPT 2 months, 3rd Thursday are
       handled properly.  Finally, the -R argument  to  calendar_scandate  directly  provides  an
       anchor for relative calculations.

       The periods handled, with possible abbreviations are:

       Years  years,  yrs,  ys,  year,  yr,  y, yearly.  A year is 365.25 days unless there is an

       Months months, mons, mnths, mths, month, mon, mnth, mth, monthly.  Note that  m,  ms,  mn,
              mns  are ambiguous and are not handled.  A month is a period of 30 days rather than
              a calendar month unless there is an anchor.

       Weeks  weeks, wks, ws, week, wk, w, weekly

       Days   days, dys, ds, day, dy, d, daily

       Hours  hours, hrs, hs, hour, hr, h, hourly

              minutes, mins, minute, min, but not m, ms, mn or mns

              seconds, secs, ss, second, sec, s

       Spaces between the numbers are optional, but are required between items, although a  comma
       may be used (with or without spaces).

       The  forms  yearly  to  hourly allow the number to be omitted; it is assumed to be 1.  For
       example, 1 d and daily are equivalent.  Note  that  using  those  forms  with  plurals  is
       confusing;  2  yearly  is the same as 2 years, not twice yearly, so it is recommended they
       only be used without numbers.

       When an anchor time is present, there is an extension to handle regular events in the form
       of  the  nth  someday of the month.  Such a specification must occur immediately after any
       year and month specification, but before any  time  of  day,  and  must  be  in  the  form
       n(th|st|rd)  day,  for  example  1st  Tuesday or 3rd Monday.  As in other places, days are
       matched case insensitively, must be in English, and  only  the  first  three  letters  are
       significant  except  that a form beginning `month' does not match `Monday'.  No attempt is
       made to sanitize the resulting date; attempts to squeeze too many occurrences into a month
       will  push  the day into the next month (but in the obvious fashion, retaining the correct
       day of the week).

       Here are some examples:

              30 years 3 months 4 days 3:42:41
              14 days 5 hours
              Monthly, 3rd Thursday

       Here is an example calendar file.  It uses a consistent date format, as recommended above.

              Feb 1, 2006 14:30 Pointless bureaucratic meeting
              Mar 27, 2006 11:00 Mutual recrimination and finger pointing
                Bring water pistol and waterproofs
              Mar 31, 2006 14:00 Very serious managerial pontification
                # UID 12C7878A9A50
              Apr 10, 2006 13:30 Even more pointless blame assignment exercise WARN 30 mins
              May 18, 2006 16:00 Regular moaning session RPT monthly, 3rd Thursday

       The second entry has a continuation line.  The third entry has a  continuation  line  that
       will  not  be shown when the entry is displayed, but the unique identifier will be used by
       the calendar_add function when updating the  event.   The  fourth  entry  will  produce  a
       warning  30  minutes before the event (to allow you to equip yourself appropriately).  The
       fifth entry repeats after a month on the 3rd Thursday, i.e. June 15,  2006,  at  the  same


       This section describes functions that are designed to be called directly by the user.  The
       first part describes those functions associated with the user's calendar; the second  part
       describes the use in glob qualifiers.

   Calendar system functions
       calendar [ -abdDsv ] [ -C calfile ] [ -n num ] [ -S showprog ] [ [ start ] end ](
       calendar -r [ -abdDrsv ] [ -C calfile ] [ -n num ] [ -S showprog ] [ start ]
              Show events in the calendar.

              With  no  arguments,  show events from the start of today until the end of the next
              working day after today.  In other words, if today is Friday, Saturday, or  Sunday,
              show up to the end of the following Monday, otherwise show today and tomorrow.

              If end is given, show events from the start of today up to the time and date given,
              which is in the format described in the previous section.  Note that if this  is  a
              date  the  time  is  assumed  to  be  midnight  at  the  start of the date, so that
              effectively this shows all events before the given date.

              end may start with a +, in which case the  remainder  of  the  specification  is  a
              relative  time  format as described in the previous section indicating the range of
              time from the start time that is to be included.

              If start is also given, show events starting from that time and date.  The word now
              can be used to indicate the current time.

              To  implement  an  alert  when events are due, include calendar -s in your ~/.zshrc


              -a     Show all items in the calendar, regardless of the start and end.

              -b     Brief:  don't display continuation lines (i.e. indented lines following  the
                     line with the date/time), just the first line.

              -B lines
                     Brief:  display at most the first lines lines of the calendar entry.  `-B 1'
                     is equivalent to `-b'.

              -C calfile
                     Explicitly specify a calendar file instead of the value of the calendar-file
                     style or the default ~/calendar.

              -d     Move  any events that have passed from the calendar file to the "done" file,
                     as given by the done-file style or the default which is  the  calendar  file
                     with .done appended.  This option is implied by the -s option.

              -D     Turns off the option -d, even if the -s option is also present.

              -n num, -num
                     Show at least num events, if present in the calendar file, regardless of the
                     start and end.

              -r     Show all the remaining options in the calendar, ignoring the given end time.
                     The start time is respected; any argument given is treated as a start time.

              -s     Use  the  shell's sched command to schedule a timed event that will warn the
                     user when an event is due.  Note that the sched command  only  runs  if  the
                     shell  is  at  an interactive prompt; a foreground task blocks the scheduled
                     task from running until it is finished.

                     The timed event usually runs the programme calendar_show to show the  event,
                     as described in the section UTILITY FUNCTIONS below.

                     By  default,  a warning of the event is shown five minutes before it is due.
                     The warning period can be configured by the style warn-time or for a  single
                     calendar  entry  by  including  WARN reltime in the first line of the entry,
                     where reltime is one of the usual relative time formats.

                     A repeated event may be indicated by including RPT reldate in the first line
                     of  the  entry.   After  the  scheduled  event has been displayed it will be
                     re-entered into the calendar file at  a  time  reldate  after  the  existing
                     event.   Note  that this is currently the only use made of the repeat count,
                     so that it is not possible to query the schedule  for  a  recurrence  of  an
                     event in the calendar until the previous event has passed.

                     If  RPT  is used, it is also possible to specify that certain recurrences of
                     an event are rescheduled or cancelled.  This is  done  with  the  OCCURRENCE
                     keyword,  followed  by whitespace and the date and time of the occurrence in
                     the regular sequence, followed by whitespace and either the date and time of
                     the  rescheduled event or the exact string CANCELLED.  In this case the date
                     and time must be in exactly the "date with local time" format  used  by  the
                     text/calendar  MIME  type  (RFC 2445), <YYYY><MM><DD>T<hh><mm><ss> (note the
                     presence  of  the  literal  character  T).   The  first  word  (the  regular
                     recurrence)  may be something other than a proper date/time to indicate that
                     the event is additional to the normal sequence; a  convention  that  retains
                     the formatting appearance is XXXXXXXXTXXXXXX.

                     Furthermore, it is useful to record the next regular recurrence (as then the
                     displayed date may be  for  a  rescheduled  event  so  cannot  be  used  for
                     calculating  the  regular  sequence).  This is specified by RECURRENCE and a
                     time or date in the same format.  calendar_add adds such an indication  when
                     it  encounters  a  recurring  event  that does not include one, based on the
                     headline date/time.

                     If calendar_add is used to update  occurrences  the  UID  keyword  described
                     there  should be present in both the existing entry and the added occurrence
                     in order to identify recurring event sequences.

                     For example,

                            Thu May 6, 2010 11:00 Informal chat RPT 1 week
                              # RECURRENCE 20100506T110000
                              # OCCURRENCE 20100513T110000 20100513T120000
                              # OCCURRENCE 20100520T110000 CANCELLED

                     The event that occurs at 11:00 on 13th  May  2010  is  rescheduled  an  hour
                     later.   The  event  that occurs a week later is cancelled.  The occurrences
                     are given on a continuation line starting with a #  character  so  will  not
                     usually be displayed as part of the event.  As elsewhere, no account of time
                     zones is taken with the times. After the  next  event  occurs  the  headline
                     date/time  will  be  `Thu May 13, 2010 12:00' while the RECURRENCE date/time
                     will be `20100513T110000' (note that cancelled  and  moved  events  are  not
                     taken  account  of  in  the  RECURRENCE, which records what the next regular
                     recurrence is, but they are accounted for in the headline date/time).

                     It is safe to run calendar -s  to  reschedule  an  existing  event  (if  the
                     calendar  file  has  changed,  for  example), and also to have it running in
                     multiples instances of the shell since the calendar file is locked  when  in

                     By  default, expired events are moved to the "done" file; see the -d option.
                     Use -D to prevent this.

              -S showprog
                     Explicitly specify a programme to be used for showing events instead of  the
                     value of the show-prog style or the default calendar_show.

              -v     Verbose:   show more information about stages of processing.  This is useful
                     for confirming that the function has successfully parsed the  dates  in  the
                     calendar file.

       calendar_add [ -BL ] event ...
              Adds  a  single  event  to the calendar in the appropriate location.  The event can
              contain multiple lines, as described in the section  Calendar  File  Format  above.
              Using  this  function  ensures  that  the  calendar file is sorted in date and time
              order.  It also makes special  arrangements  for  locking  the  file  while  it  is
              altered.  The old calendar is left in a file with the suffix .old.

              The  option  -B  indicates that backing up the calendar file will be handled by the
              caller and should not be performed by calendar_add.  The option -L  indicates  that
              calendar_add  does  not  need  to  lock  the calendar file as it is already locked.
              These options will not usually be needed by users.

              If the style reformat-date is true, the date and time of  the  new  entry  will  be
              rewritten  into  the  standard date format:  see the descriptions of this style and
              the style date-format.

              The function can use a unique identifier stored with  each  event  to  ensure  that
              updates  to  existing  events  are treated correctly.  The entry should contain the
              word UID, followed by  whitespace,  followed  by  a  word  consisting  entirely  of
              hexadecimal  digits  of  arbitrary  length  (all  digits are significant, including
              leading zeroes).  As the UID is not directly useful to the user, it  is  convenient
              to hide it on an indented continuation line starting with a #, for example:

                     Aug 31, 2007 09:30  Celebrate the end of the holidays
                       # UID 045B78A0

              The second line will not be shown by the calendar function.

              It  is  possible  to  specify  the  RPT  keyword followed by CANCELLED instead of a
              relative time.  This causes any matched event or series of events to  be  cancelled
              (the  original  event  does  not  have  to  be  marked  as recurring in order to be
              cancelled by this method).  A UID is required in order to match an  existing  event
              in the calendar.

              calendar_add will attempt to manage recurrences and occurrences of repeating events
              as described for event scheduling by calendar -s above.  To reschedule or cancel  a
              single  event calendar_add should be called with an entry that includes the correct
              UID but does not include the RPT keyword as this is taken to mean the entry applies
              to  a series of repeating events and hence replaces all existing information.  Each
              rescheduled or cancelled occurrence must have an OCCURRENCE keyword  in  the  entry
              passed  to  calendar_add which will be merged into the calendar file.  Any existing
              reference to the occurrence is replaced.  An occurrence that does not  refer  to  a
              valid existing event is added as a one-off occurrence to the same calendar entry.

              This  calls  the  user's editor to edit the calendar file.  If there are arguments,
              they are taken as the editor to use (the file name is appended  to  the  commands);
              otherwise,  the  editor  is given by the variable VISUAL, if set, else the variable

              If the calendar scheduler was running, then after editing the file calendar  -s  is
              called to update it.

              This  function  locks  out the calendar system during the edit.  Hence it should be
              used to edit the calendar file if there is any  possibility  of  a  calendar  event
              occurring  meanwhile.   Note this can lead to another shell with calendar functions
              enabled hanging waiting for a lock, so it is necessary to quit the editor  as  soon
              as possible.

       calendar_parse calendar-entry
              This is the internal function that analyses the parts of a calendar entry, which is
              passed as the only argument.  The function returns status 1 if the  argument  could
              not  be  parsed  as  a calendar entry and status 2 if the wrong number of arguments
              were passed; it also sets the  parameter  reply  to  an  empty  associative  array.
              Otherwise,  it returns status 0 and sets elements of the associative array reply as
       time   The time as a string of digits in the same units as $EPOCHSECONDS
              The regularly scheduled time.  This may differ from the actual event time  time  if
              this  is a recurring event and the next occurrence has been rescheduled.  Then time
              gives the actual time and schedtime the  time  of  the  regular  recurrence  before
       text1  The  text from the line not including the date and time of the event, but including
              any WARN or RPT keywords and values.
              Any warning time given by the WARN keyword as a string  of  digits  containing  the
              time  at  which  to  warn  in  the  same  units as $EPOCHSECONDS.  (Note this is an
              absolute time, not the relative time passed down.)  Not set  no  WARN  keyword  and
              value were matched.
              The raw string matched after the WARN keyword, else unset.
              Any  recurrence  time given by the RPT keyword as a string of digits containing the
              time of the recurrence in the same  units  as  $EPOCHSECONDS.   (Note  this  is  an
              absolute time.)  Not set if no RPT keyword and value were matched.
              The  next  regularly scheduled occurrence of a recurring event before modification.
              This may differ from rpttime, which is the actual time of the event that  may  have
              been rescheduled from the regular time.
       rptstr The raw string matched after the RPT keyword, else unset.
       text2  The text from the line after removal of the date and any keywords and values.  )

       calendar_showdate [ -r ] [ -f fmt ] date-spec ...
              The given date-spec is interpreted and the corresponding date and time printed.  If
              the initial date-spec begins with a + or - it is treated as relative to the current
              time;  date-specs after the first are treated as relative to the date calculated so
              far and a leading + is optional in that case.  This allows one to use the system as
              a date calculator.  For example, calendar_showdate '+1 month, 1st Friday' shows the
              date of the first Friday of next month.

              With the option -r nothing is printed but the value of the date and time in seconds
              since the epoch is stored in the parameter REPLY.

              With the option -f fmt the given date/time conversion format is passed to strftime;
              see notes on the date-format style below.

              In order to avoid ambiguity with negative  relative  date  specifications,  options
              must  occur  in separate words; in other words, -r and -f should not be combined in
              the same word.

              Sorts the calendar file into date and time order.    The old calendar is left in  a
              file with the suffix .old.

   Glob qualifiers
       The  function  age can be autoloaded and use separately from the calendar system, although
       it uses the function calendar_scandate for date  formatting.   It  requires  the  zsh/stat
       builtin, but uses only the builtin zstat.

       age  selects  files  having  a  given  modification time for use as a glob qualifier.  The
       format of the date is the same as that understood by the calendar system, described in the
       section FILE AND DATE FORMATS above.

       The  function  can  take  one  or  two arguments, which can be supplied either directly as
       command or arguments, or separately as shell parameters.

              print *(e:age 2006/10/04 2006/10/09:)

       The example above matches all files modified between the start of those dates.  The second
       argument may alternatively be a relative time introduced by a +:

              print *(e:age 2006/10/04 +5d:)

       The example above is equivalent to the previous example.

       In  addition  to  the  special use of days of the week, today and yesterday, times with no
       date may be specified; these apply to  today.   Obviously  such  uses  become  problematic
       around midnight.

              print *(e-age 12:00 13:30-)

       The example above shows files modified between 12:00 and 13:00 today.

              print *(e:age 2006/10/04:)

       The  example  above  matches  all  files modified on that date.  If the second argument is
       omitted it is taken to be exactly 24 hours after the first argument  (even  if  the  first
       argument contains a time).

              print *(e-age 2006/10/04:10:15 2006/10/04:10:45-)

       The  example  above  supplies  times.   Note  that  whitespace  within  the  time and date
       specification must be quoted to ensure age receives the correct arguments, hence  the  use
       of the additional colon to separate the date and time.

              print *(+age)

       This  shows the same example before using another form of argument passing.  The dates and
       times in the parameters AGEREF1 and AGEREF2 stay  in  effect  until  unset,  but  will  be
       overridden  if  any  argument  is  passed  as  an  explicit argument to age.  Any explicit
       argument causes both parameters to be ignored.


       The zsh style mechanism using the zstyle command is describe in  zshmodules(1).   This  is
       the same mechanism used in the completion system.

       The  styles  below  are  all  examined  in  the  context  :datetime:function:, for example

              The location of the main calendar.  The default is ~/calendar.

              A strftime format string  (see  strftime(3))  with  the  zsh  extensions  providing
              various  numbers  with  no leading zero or space if the number is a single digit as
              described for the %D{string} prompt format  in  the  section  EXPANSION  OF  PROMPT
              SEQUENCES in zshmisc(1).

              This  is  used  for outputting dates in calendar, both to support the -v option and
              when adding recurring events back to the calendar file, and in calendar_showdate as
              the final output format.

              If  the style is not set, the default used is similar the standard system format as
              output by the date command (also known as `ctime format'): `%a %b  %d  %H:%M:%S  %Z

              The  location  of  the  file  to  which events which have passed are appended.  The
              default is the calendar file location with the suffix .done.  The style may be  set
              to an empty string in which case a "done" file will not be maintained.

              Boolean,  used  by  calendar_add.   If it is true, the date and time of new entries
              added to the calendar will  be  reformatted  to  the  format  given  by  the  style
              date-format  or  its  default.   Only  the  date  and  time  of the event itself is
              reformatted; any subsidiary dates and times such as those  associated  with  repeat
              and warning times are left alone.

              The programme run by calendar for showing events.  It will be passed the start time
              and stop time of the events requested in seconds since the epoch  followed  by  the
              event  text.   Note  that  calendar -s uses a start time and stop time equal to one
              another to indicate alerts for specific events.

              The default is the function calendar_show.

              The time before an event at which a warning will be displayed, if the first line of
              the event does not include the text EVENT reltime.  The default is 5 minutes.


              Attempt  to lock the files given in the argument.  To prevent problems with network
              file locking this is done in an ad hoc fashion by attempting to create  a  symbolic
              link  to the file with the name file.lockfile.  No other system level functions are
              used for locking, i.e. the file can be accessed and modified by  any  utility  that
              does not use this mechanism.  In particular, the user is not prevented from editing
              the calendar file at the same time unless calendar_edit is used.

              Three attempts are made  to  lock  the  file  before  giving  up.   If  the  module
              zsh/zselect  is  available, the times of the attempts are jittered so that multiple
              instances of the calling function are unlikely to retry at the same time.

              The files locked are appended to the array lockfiles, which should be local to  the

              If all files were successfully locked, status zero is returned, else status one.

              This  function  may  be used as a general file locking function, although this will
              only work if only this mechanism is used to lock files.

              This is a backend used by various other functions to parse the calendar file, which
              is  passed  as the only argument.  The array calendar_entries is set to the list of
              events in the file; no pruning is done except that ampersands are removed from  the
              start of the line.  Each entry may contain multiple lines.

              This  is  a  generic  function to parse dates and times that may be used separately
              from the calendar system.   The  argument  is  a  date  or  time  specification  as
              described  in  the section FILE AND DATE FORMATS above.  The parameter REPLY is set
              to the number of seconds since the epoch corresponding to that date  or  time.   By
              default, the date and time may occur anywhere within the given argument.

              Returns status zero if the date and time were successfully parsed, else one.

              -a     The  date  and time are anchored to the start of the argument; they will not
                     be matched if there is preceding text.

              -A     The date and time are anchored to both the start and end  of  the  argument;
                     they will not be matched if the is any other text in the argument.

              -d     Enable additional debugging output.

              -m     Minus.   When  -R  anchor_time is also given the relative time is calculated
                     backwards from anchor_time.

              -r     The argument passed is to be parsed as a relative time.

              -R anchor_time
                     The argument passed is to be  parsed  as  a  relative  time.   The  time  is
                     relative to anchor_time, a time in seconds since the epoch, and the returned
                     value is the absolute time corresponding to  advancing  anchor_time  by  the
                     relative  time  given.   This allows lengths of months to be correctly taken
                     into account.  If the final day does not exist in the given month, the  last
                     day  of the final month is given.  For example, if the anchor time is during
                     31st January 2007 and the relative time is 1 month, the final  time  is  the
                     same time of day during 28th February 2007.

              -s     In  addition  to  setting REPLY, set REPLY2 to the remainder of the argument
                     after the date and time have been stripped.  This is empty if the option  -A
                     was given.

              -t     Allow  a  time with no date specification.  The date is assumed to be today.
                     The behaviour is unspecified if the  iron  tongue  of  midnight  is  tolling

              The  function  used  by default to display events.  It accepts a start time and end
              time for events, both in epoch seconds, and an event description.

              The event is always printed to standard output.  If  the  command  line  editor  is
              active  (which will usually be the case) the command line will be redisplayed after
              the output.

              If the parameter DISPLAY  is  set  and  the  start  and  end  times  are  the  same
              (indicating a scheduled event), the function uses the command xmessage to display a
              window with the event details.


       As the system is based entirely on  shell  functions  (with  a  little  support  from  the
       zsh/datetime  module)  the  mechanisms  used  are  not  as  robust  as those provided by a
       dedicated calendar utility.  Consequently the user should not rely on the shell for  vital

       There is no calendar_delete function.

       There  is no localization support for dates and times, nor any support for the use of time

       Relative periods of months and years do not take into account the variable number of days.

       The calendar_show function is currently hardwired to use xmessage for displaying alerts on
       X  Window  System displays.  This should be configurable and ideally integrate better with
       the desktop.

       calendar_lockfiles hangs the shell while waiting for a lock on a file.  If called  from  a
       scheduled task, it should instead reschedule the event that caused it.