cron parser

Library for parsing cron expressions with timezone support.

Example:

use chrono::{TimeZone, Utc};
use chrono_tz::Europe::Lisbon;
use cron_parser::parse;

fn main() {
   if let Ok(next) = parse("*/5 * * * *", &Utc::now()) {
        println!("when: {}", next);
   }

   // passing a custom timestamp
   if let Ok(next) = parse("0 0 29 2 *", &Utc.timestamp(1893456000, 0)) {
        println!("next leap year: {}", next);
        assert_eq!(next.timestamp(), 1961625600);
   }

   assert!(parse("2-3,9,*/15,1-8,11,9,4,5 * * * *", &Utc::now()).is_ok());
   assert!(parse("* * * * */Fri", &Utc::now()).is_err());

   // use custom timezone
   assert!(parse("*/5 * * * *", &Utc::now().with_timezone(&Lisbon)).is_ok());
}

Cron table:

# ┌─────────────────────  minute (0 - 59)
# │ ┌───────────────────  hour   (0 - 23)
# │ │ ┌─────────────────  dom    (1 - 31) day of month
# │ │ │ ┌───────────────  month  (1 - 12)
# │ │ │ │ ┌─────────────  dow    (0 - 6 or Sun - Sat)  day of week (Sunday to Saturday)
# │ │ │ │ │
# │ │ │ │ │
# │ │ │ │ │
# * * * * * <command to execute>

Field	Required	Allowed values	Allowed special characters
Minutes	Yes	0–59	* , - /
Hours	Yes	0–23	* , - /
Day of month	Yes	1–31	* , - /
Month	Yes	1–12	* , - /
Day of week	Yes	0–6 or Sun-Sat	* , - /

For the day of the week, when using a Weekday (Sun-Sat) the expression */Day is not supported instead use the integer, reasons for this is that for example */Wed = */3 translates to run every 3rd day of week, this means Sunday, Wednesday, Saturday.

• * any value
• , value list separator
• - range of values
• / step values

start-end/step

Ranges with steps are supported, for example:

0 12-18/3 * * *  # every 3 hours starting from 12 to 18

Or every 6 hours starting from 1:

0 1/6 * * *

Depends on crate chrono.

Example of Cargo.toml:

[dependencies]
chrono = "^0.4"
cron-parser = "*"

Getting the next 10 leap year iterations:

use chrono::{DateTime, Utc};
use cron_parser::parse;

fn main() {
    let now = Utc::now();
    let mut crons = Vec::<DateTime<Utc>>::new();
    let mut next = parse("0 0 29 2 *", &now).unwrap();
    for _ in 0..10 {
        next = parse("0 0 29 2 *", &next).unwrap();
        crons.push(next);
    }
    for x in crons {
        println!("{} - {}", x, x.timestamp());
    }
}

It will print something like:

2024-02-29 00:00:00 UTC - 1709164800
2028-02-29 00:00:00 UTC - 1835395200
2032-02-29 00:00:00 UTC - 1961625600
2036-02-29 00:00:00 UTC - 2087856000
2040-02-29 00:00:00 UTC - 2214086400
2044-02-29 00:00:00 UTC - 2340316800
2048-02-29 00:00:00 UTC - 2466547200
2052-02-29 00:00:00 UTC - 2592777600
2056-02-29 00:00:00 UTC - 2719008000
2060-02-29 00:00:00 UTC - 2845238400