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