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.