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vincent 2016-01-04 11:57:55 +01:00
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The following is greatly inspired by python-crontab (https://pypi.python.org/pypi/python-crontab), Wikipedia (https://en.wikipedia.org/wiki/Cron#CRON_expression).
Field Name Mandatory Allowed Values Special Characters Extra Values
Minutes Yes 0-59 * / , - < >
Hours Yes 0-23 * / , - < >
Day of month Yes 1-31 * / , - < >
Month Yes 1-12 or JAN-DEC * / , - < >
Day of week Yes 0-6 or SUN-SAT * / , - < >
Year No 2015-2100 * , -
Extra Values are < for minimum value, such as 0 for minutes or 1 for
months. And > for maximum value, such as 23 for hours or 12 for
months.
Supported special cases allow crontab lines to not use fields. These
are the supported aliases which are not available in SystemV mode:
Case Meaning
@reboot Every boot
@hourly 0 * * * *
@daily 0 0 * * *
@weekly 0 0 * * 0
@monthly 0 0 1 * *
@yearly 0 0 1 1 *
@annually 0 0 1 1 *
@midnight 0 0 * * *
Comma ( , ) Commas are used to separate items of a list. For example,
using "MON,WED,FRI" in the 5th field (day of week) means Mondays,
Wednesdays and Fridays.
Hyphen ( - ) Hyphens define ranges. For example, 2000-2010 indicates
every year between 2000 and 2010 AD, inclusive.
Percent ( % ) Percent-signs (%) in the command, unless escaped with
backslash (\), are changed into newline characters, and all data
after the first % are sent to the command as standard input.
L 'L' stands for "last". When used in the day-of-week field, it allows
you to specify constructs such as "the last Friday" ("5L") of a
given month. In the day-of-month field, it specifies the last day
of the month.
W The 'W' character is allowed for the day-of-month field. This
character is used to specify the weekday (Monday-Friday) nearest
the given day. As an example, if you were to specify "15W" as the
value for the day-of-month field, the meaning is: "the nearest
weekday to the 15th of the month." So, if the 15th is a Saturday,
the trigger fires on Friday the 14th. If the 15th is a Sunday, the
trigger fires on Monday the 16th. If the 15th is a Tuesday, then
it fires on Tuesday the 15th. However, if you specify "1W" as the
value for day-of-month, and the 1st is a Saturday, the trigger
fires on Monday the 3rd, as it does not 'jump' over the boundary
of a month's days. The 'W' character can be specified only when
the day-of-month is a single day, not a range or list of days.
Hash ( # ) '#' is allowed for the day-of-week field, and must be
followed by a number between one and five. It allows you to
specify constructs such as "the second Friday" of a given
month.[13]
Question mark ( ? ) In some implementations, used instead of '*' for
leaving either day-of-month or day-of-week blank. Other cron
implementations substitute "?" with the start-up time of the cron
daemon, so that ? ? * * * * would be updated to 25 8 * * * * if
cron started-up on 8:25am, and would run at this time every day
until restarted again.[14]
(WON'T BE IMPLEMENTED)
Slash ( / ) In vixie-cron, slashes can be combined with ranges to
specify step values.[6] For example, */5 in the minutes field
indicates every 5 minutes (see note). It is shorthand for the more
verbose POSIX form 5,10,15,20,25,30,35,40,45,50,55,00. POSIX does
not define a use for slashes; its rationale (commenting on a BSD
extension) notes that the definition is based on System V format
but does not exclude the possibility of extensions.[5]