ZSHCALSYS(1) User Commands ZSHCALSYS(1)

NAME

zshcalsys - zsh calendar system

DESCRIPTION

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 functions age, before and after are provided that can be
used in a glob qualifier; they allow 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 file.

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.

FILE AND DATE FORMATS

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.

+o 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.

+o 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
2007/04/03:13:13
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:

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

+o 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, before and after functions) 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 understood:

+0100
GMT
GMT-7
CET+1CDT

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:

+o YYYY/MM/DD

+o YYYY-MM-DD

+o YYYY/MNM/DD

+o YYYY-MNM-DD

+o DD[th|st|rd] MNM[,] [ YYYY ]

+o MNM DD[th|st|rd][,] [ YYYY ]

+o DD[th|st|rd]/MM[,] YYYY

+o DD[th|st|rd]/MM/YYYY

+o MM/DD[th|st|rd][,] YYYY

+o 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 anchor.

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

Seconds
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
4d,10hr

Example

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 time.

USER FUNCTIONS

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 file.

Options:

-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
use.

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.

calendar_edit
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
EDITOR.

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 follows:

time The time as a string of digits in the same units as
$EPOCHSECONDS
schedtime
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 modification.
text1 The text from the line not including the date and time
of the event, but including any WARN or RPT keywords
and values.
warntime
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.
warnstr
The raw string matched after the WARN keyword, else
unset.
rpttime
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.
schedrpttime
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.

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

Glob qualifiers

age 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.

AGEREF=2006/10/04:10:15
AGEREF2=2006/10/04:10:45
print *(+age)

This shows the same example before using another form of
argument passing. The dates and times in the parameters
AGEREF 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.

Instead of an explicit date and time, it's possible to use the
modification time of a file as the date and time for either
argument by introducing the file name with a colon:

print *(e-age :file1-)

matches all files created on the same day (24 hours starting
from midnight) as file1.

print *(e-age :file1 :file2-)

matches all files modified no earlier than file1 and no later
than file2; precision here is to the nearest second.

after
before The functions after and before are simpler versions of age
that take just one argument. The argument is parsed similarly
to an argument of age; if it is not given the variable AGEREF
is consulted. As the names of the functions suggest, a file
matches if its modification time is after or before the time
and date specified. If a time only is given the date is
today.

The two following examples are therefore equivalent:
print *(e-after 12:00-)
print *(e-after today:12:00-)

STYLES

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 :datetime:calendar:.

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

date-format
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 %Y'.

done-file
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.

reformat-date
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.

show-prog
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.

warn-time
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.

UTILITY FUNCTIONS

calendar_lockfiles
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 caller.

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.

calendar_read
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.

calendar_scandate
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.

Options:
-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 twelve.

calendar_show
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.

BUGS

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 alerts.

There is no calendar_delete function.

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

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.

zsh 5.9 May 14, 2022 ZSHCALSYS(1)