diary-file is a variable defined in `calendar.el'.
Its value is

Name of the file in which one's personal diary of dates is kept.

The file's entries are lines beginning with any of the forms
specified by the variable `diary-date-forms', which by default
uses the forms of `diary-american-date-forms':


with the remainder of the line being the diary entry string for
that date. MONTH and DAY are one or two digit numbers, YEAR is a
number and may be written in full or abbreviated to the final two
digits (if `diary-abbreviated-year-flag' is non-nil). MONTHNAME
and DAYNAME can be spelled in full (as specified by the variables
`calendar-month-name-array' and `calendar-day-name-array'), or
abbreviated (as specified by `calendar-month-abbrev-array' and
`calendar-day-abbrev-array') with or without a period. Case is
ignored. Any of DAY, MONTH, or MONTHNAME, YEAR can be `*' which
matches any day, month, or year, respectively. If the date does
not contain a year, it is generic and applies to any year. A
DAYNAME entry applies to the appropriate day of the week in every week.

You can customize `diary-date-forms' to your preferred format.
Three default styles are provided: `diary-american-date-forms',
`diary-european-date-forms', and `diary-iso-date-forms'.
You can choose between these by setting `calendar-date-style' in your
init file, or by using `calendar-set-date-style' when in the calendar.

A diary entry can be preceded by the character `diary-nonmarking-symbol'
(ordinarily `&') to make that entry nonmarking--that is, it will not be
marked on dates in the calendar window but will appear in a diary window.

Multiline diary entries are made by indenting lines after the first with
either a TAB or one or more spaces.

Lines not in one the above formats are ignored. Here are some sample diary
entries (in the default American style):

12/22/1988 Twentieth wedding anniversary!!
&1/1. Happy New Year!
10/22 Ruth's birthday.
21: Payday
Tuesday--weekly meeting with grad students at 10am
Supowit, Shen, Bitner, and Kapoor to attend.
1/13/89 Friday the thirteenth!!
&thu 4pm squash game with Lloyd.
mar 16 Dad's birthday
April 15, 1989 Income tax due.
&* 15 time cards due.

If the first line of a diary entry consists only of the date or day name with
no trailing blanks or punctuation, then that line is not displayed in the
diary window; only the continuation lines is shown. For example, the
single diary entry

Bill Blattner visits Princeton today
2pm Cognitive Studies Committee meeting
2:30-5:30 Lizzie at Lawrenceville for `Group Initiative'
4:00pm Jamie Tappenden
7:30pm Dinner at George and Ed's for Alan Ryan
7:30-10:00pm dance at Stewart Country Day School

will appear in the diary window without the date line at the beginning. This
facility allows the diary window to look neater, but can cause confusion if
used with more than one day's entries displayed.

Diary entries can be based on Lisp sexps. For example, the diary entry

%%(diary-block 11 1 1990 11 10 1990) Vacation

causes the diary entry "Vacation" to appear from November 1 through
November 10, 1990. See the documentation for the function
`diary-list-sexp-entries' for more details.

Diary entries based on the Hebrew, the Islamic and/or the Bahá'í
calendar are also possible, but because these are somewhat slow, they
are ignored unless you set the `diary-nongregorian-listing-hook' and
the `diary-nongregorian-marking-hook' appropriately. See the
documentation of these hooks for details.

Diary files can contain directives to include the contents of other files; for
details, see the documentation for the variable `diary-list-entries-hook'.

You can customize this variable.