moving command line utility here
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gorhill
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@ -6,7 +6,7 @@ In another project, I decided to use cron expression syntax to encode scheduling
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The time-matching algorithm in this implementation is efficient, it avoids as much as possible to guess the next matching time stamp, a common technique seen in a number of implementations out there.
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The time-matching algorithm in this implementation is efficient, it avoids as much as possible to guess the next matching time stamp, a common technique seen in a number of implementations out there.
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There is also a companion command-line utility to evaluate cron time expressions: <https://github.com/gorhill/cronexprdo> (which of course uses this library).
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There is also a companion command-line utility to evaluate cron time expressions: <https://github.com/gorhill/cronexpr/cronexpr> (which of course uses this library).
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Implementation
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Implementation
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--------------
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--------------
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@ -0,0 +1,122 @@
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cronexpr: command-line utility
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==============================
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A command-line utility written in Go to evaluate cron time expressions.
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It is based on the standalone Go library <https://github.com/gorhill/cronexpr>.
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## Install
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go get github.com/gorhill/cronexpr
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go install github.com/gorhill/cronexpr
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## Usage
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cronexpr [options] "{cron expression}"
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## Options
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`-l`:
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Go-compliant time layout to use for outputting time value(s), see <http://golang.org/pkg/time/#pkg-constants>.
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Default is `"Mon, 02 Jan 2006 15:04:05 MST"`
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`-n`:
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Number of resulting time values to output.
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Default is 1.
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`-t`:
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Whole or partial RFC3339 time value (i.e. `2006-01-02T15:04:05Z07:00`) against which the cron expression is evaluated. Examples of valid values include (assuming EST time zone):
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`13` = 2013-01-01T00:00:00-05:00
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`2013` = 2013-01-01T00:00:00-05:00
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`2013-08` = 2013-08-01T00:00:00-05:00
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`2013-08-31` = 2013-08-31T00:00:00-05:00
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`2013-08-31T12` = 2013-08-31T12:00:00-05:00
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`2013-08-31T12:40` = 2013-08-31T12:40:00-05:00
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`2013-08-31T12:40:35` = 2013-08-31T12:40:35-05:00
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`2013-08-31T12:40:35-10:00` = 2013-08-31T12:40:35-10:00
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Default time is current time, and default time zone is local time zone.
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## Examples
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#### Example 1
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Midnight on December 31st of any year.
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Command:
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cronexpr -t="2013-08-31" -n=5 "0 0 31 12 *"
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Output (assuming computer is in EST time zone):
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# "0 0 31 12 *" + "2013-08-31T00:00:00-04:00" =
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Tue, 31 Dec 2013 00:00:00 EST
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Wed, 31 Dec 2014 00:00:00 EST
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Thu, 31 Dec 2015 00:00:00 EST
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Sat, 31 Dec 2016 00:00:00 EST
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Sun, 31 Dec 2017 00:00:00 EST
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#### Example 2
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2pm on February 29th of any year.
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Command:
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cronexpr -t=2000 -n=10 "0 14 29 2 *"
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Output (assuming computer is in EST time zone):
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# "0 14 29 2 *" + "2000-01-01T00:00:00-05:00" =
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Tue, 29 Feb 2000 14:00:00 EST
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Sun, 29 Feb 2004 14:00:00 EST
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Fri, 29 Feb 2008 14:00:00 EST
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Wed, 29 Feb 2012 14:00:00 EST
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Mon, 29 Feb 2016 14:00:00 EST
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Sat, 29 Feb 2020 14:00:00 EST
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Thu, 29 Feb 2024 14:00:00 EST
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Tue, 29 Feb 2028 14:00:00 EST
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Sun, 29 Feb 2032 14:00:00 EST
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Fri, 29 Feb 2036 14:00:00 EST
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#### Example 3
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12pm on the work day closest to the 15th of March and every three month
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thereafter.
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Command:
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cronexpr -t=2013-09-01 -n=5 "0 12 15W 3/3 *"
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Output (assuming computer is in EST time zone):
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# "0 12 15W 3/3 *" + "2013-09-01T00:00:00-04:00" =
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Mon, 16 Sep 2013 12:00:00 EDT
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Mon, 16 Dec 2013 12:00:00 EST
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Fri, 14 Mar 2014 12:00:00 EDT
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Mon, 16 Jun 2014 12:00:00 EDT
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Mon, 15 Sep 2014 12:00:00 EDT
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#### Example 4
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Midnight on the fifth Saturday of any month (twist: not all months have a 5th
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specific day of week).
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Command:
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cronexpr -t=2013-09-02 -n 5 "0 0 * * 6#5"
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Output (assuming computer is in EST time zone):
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# "0 0 * * 6#5" + "2013-09-02T00:00:00-04:00" =
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Sat, 30 Nov 2013 00:00:00 EST
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Sat, 29 Mar 2014 00:00:00 EDT
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Sat, 31 May 2014 00:00:00 EDT
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Sat, 30 Aug 2014 00:00:00 EDT
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Sat, 29 Nov 2014 00:00:00 EST
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@ -0,0 +1,111 @@
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/*!
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* Copyright 2013 Raymond Hill
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*
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* Project: github.com/gorhill/cronexprdo
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* File: main.go
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* Version: 1.0
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* License: GPL v3 see <https://www.gnu.org/licenses/gpl.html>
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*
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*/
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package main
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/******************************************************************************/
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import (
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"flag"
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"fmt"
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"os"
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"time"
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"github.com/gorhill/cronexpr"
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)
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/******************************************************************************/
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var (
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usage = func() {
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fmt.Fprintf(os.Stderr, "usage:\n %s [options] \"{cron expression}\"\noptions:\n", os.Args[0])
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flag.PrintDefaults()
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}
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inTimeStr string
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outTimeCount uint
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outTimeLayout string
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)
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/******************************************************************************/
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func main() {
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var err error
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flag.Usage = usage
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flag.StringVar(&inTimeStr, "t", "", `whole or partial RFC3339 time value (i.e. "2006-01-02T15:04:05Z07:00") against which the cron expression is evaluated, now if not present`)
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flag.UintVar(&outTimeCount, "n", 1, `number of resulting time values to output`)
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flag.StringVar(&outTimeLayout, "l", "Mon, 02 Jan 2006 15:04:05 MST", `Go-compliant time layout to use for outputting time value(s), see <http://golang.org/pkg/time/#pkg-constants>`)
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flag.Parse()
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cronStr := flag.Arg(0)
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if len(cronStr) == 0 {
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flag.Usage()
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return
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}
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inTime := time.Now()
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inTimeLayout := ""
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timeStrLen := len(inTimeStr)
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if timeStrLen == 2 {
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inTimeLayout = "06"
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} else if timeStrLen >= 4 {
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inTimeLayout += "2006"
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if timeStrLen >= 7 {
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inTimeLayout += "-01"
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if timeStrLen >= 10 {
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inTimeLayout += "-02"
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if timeStrLen >= 13 {
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inTimeLayout += "T15"
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if timeStrLen >= 16 {
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inTimeLayout += ":04"
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if timeStrLen >= 19 {
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inTimeLayout += ":05"
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if timeStrLen >= 20 {
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inTimeLayout += "Z07:00"
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}
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}
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}
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}
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}
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}
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}
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if len(inTimeLayout) > 0 {
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// default to local time zone
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if timeStrLen < 20 {
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inTime, err = time.ParseInLocation(inTimeLayout, inTimeStr, time.Local)
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} else {
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inTime, err = time.Parse(inTimeLayout, inTimeStr)
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}
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if err != nil {
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fmt.Fprintf(os.Stderr, "# error: unparseable time value: \"%s\"\n", inTimeStr)
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os.Exit(1)
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}
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}
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expr, err := cronexpr.Parse(cronStr)
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if err != nil {
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fmt.Fprintf(os.Stderr, "# %s: %s\n", os.Args[0], err)
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os.Exit(1)
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}
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// Anything on the output which starts with '#' can be ignored if the caller
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// is interested only in the time values. There is only one time
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// value per line, and they are always in chronological ascending order.
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fmt.Printf("# \"%s\" + \"%s\" =\n", cronStr, inTime.Format(time.RFC3339))
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if outTimeCount < 1 {
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outTimeCount = 1
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}
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outTimes := expr.NextN(inTime, outTimeCount)
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for _, outTime := range outTimes {
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fmt.Println(outTime.Format(outTimeLayout))
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}
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}
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