Schedule

The names of the product elements

The name of the type

Parse a string as a schedule.

The syntax is similar to that of systemd calendar specifications (man systemd.time).

E.g. Mon..Fri *-5/2-1 *:20,34:00

meaning:

• from monday to friday (inclusive), and
• any year, and
• from may and every second month thereafter, and
• any hour, and
• minute 20 and 34, and
• second 0

The schedule is parsed in three space-separated parts:

1. a day-of-week filter
2. a date filter
3. a time filter

At least one of the of the parts must be specified, and they must be specified in order.

If a part is omitted, the following filters are assumed:

• day-of-week part => any
• date part => any
• time part => 00:00:00

In other words, if the day-of-week part is omitted, any day of week is valid, if the date part is omitted then any date is valid, and if the time part is omitted then only midnight is valid.

In the date filter, if no year is specified, then any year matched. I.e. 10-2 is equivalent to *-10-2

In the time filter, if no second is specified, then second 0 is matched. I.e. 20:30 is equivalent to 20:30:00

A filter may be either *, or a disjunction of numbers or a range. * is the wildcard filter which matches anything. A disjunction is separated by , and any of the numbers or ranges must match for the schedule to happen. A range is given as start[..step][/step] (inclusive).

Examples

Specification in extended BNF

schedule       ::= [dayofweekspec] [datespec] [timespec]
dayofweekspec  ::= dayofweekrange{,dayofweekrange}
dayofweekrange ::= dayofweek[..dayofweek]
dayofweek      ::= 'Mon' | 'Tue' | 'Wed' | 'Thu' | 'Fri' | 'Sat' | 'Sun'
datespec       ::= comps-comps | comps-comps-comps // either month-day or year-month-day
timespec       ::= comps:comps | comps:comps:comps // either hour:minute of hour:minute:second
comps          ::= comp{,comp}
comp           ::= '*' | filter
filter         ::= int[..int][/int]

Try to parse a string as a schedule, or return None if it was invalid.