From db81c0f41dd91b85d4c0557a2c267e550f8a1bf7 Mon Sep 17 00:00:00 2001 From: gorhill Date: Thu, 29 Aug 2013 19:37:04 -0400 Subject: [PATCH] fleshing out --- README.md | 63 ++++++++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 53 insertions(+), 10 deletions(-) diff --git a/README.md b/README.md index 2d67405..90b8ecb 100644 --- a/README.md +++ b/README.md @@ -1,27 +1,70 @@ cronexpression for Go ===================== +Cron expression parser in Go language (golang). -Go language (golang) cron expression parser. Given a cron expression and a time stamp, you can get the next time stamp which satisfy the cron expression. +Given a cron expression and a time stamp, you can get the next time stamp which satisfy the cron expression. +Implementation +-------------- The reference documentation for this implementation is found at -https://en.wikipedia.org/wiki/Cron#CRON_expression, with the following -differences: +https://en.wikipedia.org/wiki/Cron#CRON_expression, which I copy/pasted here (laziness) with modifications where this implementation differs: -* Supports the second field (before minute field) + Field name Mandatory? Allowed values Allowed special characters + ---------- ---------- -------------- -------------------------- + Minutes Yes 0-59 * / , - + Hours Yes 0-23 * / , - + Day of month Yes 1-31 * / , - ? L W + Month Yes 1-12 or JAN-DEC * / , - + Day of week Yes 0-6 or SUN-SAT * / , - ? L # + Year No 1970–2099 * / , - + +Asterisk ( * ) +-------------- +The asterisk indicates that the cron expression matches for all values of the field. E.g., using an asterisk in the 4th field (month) indicates every month. + +Slash ( / ) +----------- +Slashes describe increments of ranges. For example `3-59/15` in the minute field indicate the third minute of the hour and every 15 minutes thereafter. The form `*/...` is equivalent to the form "first-last/...", that is, an increment over the largest possible range of the field. + +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. + +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. + +Question mark ( ? ) +------------------- +Note: Question mark is a non-standard character and exists only in some cron implementations. It is used instead of `*` for leaving either day-of-month or day-of-week blank. + +With the following differences: + +* Supports optional second field (before minute field) * If five fields are present, a wildcard year field is appended -* If six field are present, "0" is prepended as second field -* Domain for day-of-week field is [0-7] instead of [0-6], 7 being Sunday, like zero. -* `@reboot` is not supported, as it is meaningless for a cron expression parser library -* As of now, the behavior of the code is undetermined if a malformed cron expression is supplied (most likely, code will panic) +* If six field are present, `0` is prepended as second field, that is, `* * * * * *` internally become `0 * * * * * *`. +* Domain for day-of-week field is [0-7] instead of [0-6], 7 being Sunday (like 0). +* `@reboot` is not supported +* As of now, the behavior of the code is undetermined if a malformed cron expression is supplied Install ------- - go get github.com/gorhill/cronexpression Usage ----- - Import the library: import "github.com/gorhill/cronexpression"