getdate - convert time and date from ASCII
time_t getdate(buf, now)
struct timeb *now;
Getdate is a routine that converts most common time specifications to standard UNIX for-
mat. The first argument is the character string containing the time and date; the second
is the assumed current time (used for relative specifications); if NULL is passed,
ftime(2) is used to obtain the current time and timezone.
The character string consists of 0 or more specifications of the following form:
tod A tod is a time of day, which is of the form hh:mm[:ss] (or hhmm) [meridian]
[zone]. If no meridian - am or pm - is specified, a 24-hour clock is used. A tod
may be specified as just hh followed by a meridian.
date A date is a specific month and day, and possibly a year. Acceptable formats are
mm/dd[/yy] and monthname dd[, yy] If omitted, the year defaults to the current
year; if a year is specified as a number less than 100, 1900 is added. If a number
not followed by a day or relative time unit occurs, it will be interpreted as a
year if a tod, monthname, and dd have already been specified; otherwise, it will be
treated as a tod. This rule allows the output from date(1) or ctime(3) to be
passed as input to getdate.
day A day of the week may be specified; the current day will be used if appropriate. A
day may be preceeded by a number, indicating which instance of that day is desired;
the default is 1. Negative numbers indicate times past. Some symbolic numbers are
accepted: last, next, and the ordinals first through twelfth (second is ambiguous,
and is not accepted as an ordinal number). The symbolic number next is equivalent
to 2; thus, next monday refers not to the immediately coming Monday, but to the one
a week later.
Specifications relative to the current time are also accepted. The format is [num-
ber] unit; acceptable units are year, month, fortnight, week, day, hour, minute,
The actual date is formed as follows: first, any absolute date and/or time is processed
and converted. Using that time as the base, day-of-week specifications are added; last,
relative specifications are used. If a date or day is specified, and no absolute or rela-
tive time is given, midnight is used. Finally, a correction is applied so that the cor-
rect hour of the day is produced after allowing for daylight savings time differences.
Getdate accepts most common abbreviations for days, months, etc.; in particular, it will
recognize them with upper or lower case first letter, and will recognize three-letter
abbreviations for any of them, with or without a trailing period. Units, such as weeks,
may be specified in the singular or plural. Timezone and meridian values may be in upper
or lower case, and with or without periods.
Steven M. Bellovin (unc!smb)
Dept. of Computer Science
University of North Carolina at Chapel Hill
Because yacc(1) is used to parse the date, getdate cannot be used a subroutine to any pro-
gram that also needs yacc.
The grammar and scanner are rather primitive; certain desirable and unambiguous construc-
tions are not accepted. Worse yet, the meaning of some legal phrases is not what is
expected; next week is identical to 2 weeks.
The daylight savings time correction is not perfect, and can get confused if handed times
between midnight and 2:00 am on the days that the reckoning changes.
Because localtime(2) accepts an old-style time format without zone information, attempting
to pass getdate a current time containing a different zone will probably fail.