go-cron

Cron is a system daemon used to execute desired tasks (in the background) at designated times.

Binaries can be found at: https://github.com/cravler/go-cron/releases

Usage

cron --help

crontab.yaml example:

exp: "@every 1h15m5s"
cmd:
    name: "ls"
    argv:
        - "-lah"
        - "--color=auto"
    dir: "/var/www"
log:
    # Combined output (stdout & stderr)
    file: "/var/log/app-1.log"
---
exp: "5 15 */1 * * ?"
# Skip command run, if previous still running
lock: true
cmd:
    name: "env"
    env:
        - "TEST1=123"
        - "TEST2=456 789"
log:
    # If file empty, we can specify (stdout & stderr)
    # Defaults to "".
    file: ""
    # The maximum size of the log before it is rolled.
    # A positive integer plus a modifier representing 
    # the  unit of measure (k, m, or g).
    # Defaults to 0 (unlimited).
    size: 1m
    # The maximum number of log files that can be present.
    # If rolling the logs creates excess files,
    # the oldest file is removed.
    # Only effective when size is also set.
    # A positive integer.
    # Defaults to 1.
    num: 3
stdout:
    file: "/var/log/app-2-stdout.log"
stderr:
    file: "/var/log/app-2-stderr.log"
    size: 5m
    num: 1

CRON Expression Format

A cron expression represents a set of times, using 5-6 space-separated fields.

Field name	Mandatory?	Allowed values	Allowed special characters
Seconds	No	0-59	* / , -
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	* / , - ?

Month and Day of week field values are case insensitive. SUN, Sun, and sun are equally accepted.

Special Characters

Asterisk *

The asterisk indicates that the cron expression will match for all values of the field; e.g., using an asterisk in the month field would indicate every month.

Slash /

Slashes are used to describe increments of ranges. For example 3-59/15 in the minutes field would indicate the 3rd 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. The form N/... is accepted as meaning N-MAX/..., that is, starting at N, use the increment until the end of that specific range. It does not wrap around.

Comma ,

Commas are used to separate items of a list. For example, using MON,WED,FRI in the day of week field would mean Mondays, Wednesdays and Fridays.

Hyphen -

Hyphens are used to define ranges. For example, 9-17 would indicate every hour between 9am and 5pm inclusive.

Question mark ?

Question mark may be used instead of * for leaving either day of month or day of week blank.

Predefined schedules

You may use one of several pre-defined schedules in place of a cron expression.

Entry	Description	Equivalent To
@yearly (or @annually)	Run once a year, midnight, Jan. 1st	0 0 1 1 *
@monthly	Run once a month, midnight, first of month	0 0 1 * *
@weekly	Run once a week, midnight between Sat/Sun	0 0 * * 0
@daily (or @midnight)	Run once a day, midnight	0 0 * * *
@hourly	Run once an hour, beginning of hour	0 * * * *

@every <duration>

where duration is a string with time units: s, m, h.

Entry	Description	Equivalent To
@every 5s	Run every 5 seconds	*/5 * * * * ?
@every 15m5s	Run every 15 minutes 5 seconds	5 */15 * * * ?
@every 1h15m5s	Run every 1 hour 15 minutes 5 seconds	5 15 */1 * * ?

Time zones

By default, all scheduling is done in the machine's local time zone. Individual cron schedules may also override the time zone they are to be interpreted in by providing an additional space-separated field at the beginning of the cron spec, of the form CRON_TZ=Europe/London.

For example:

exp: "CRON_TZ=Europe/London 0 6 * * ?" # Runs at 6am in Europe/London

Be aware that jobs scheduled during daylight-savings leap-ahead transitions will not be run!