Cron expression of every 3 minutes between specific time

Question

Here is the scenario:- I want to run a specific function in my NodeJs application and for that i am using NodeScheduler

I know i can use this expression

*/3 8-15 * * *

for every 3 minutes between 8 AM to 3 PM but i want to run it between 8:30 AM to 3:15 PM but Cron expression for this which i made is certainly wrong

30-15/3 8-15 * * *

does anyone know what can be correct cron expression for this scenario ?

Answer 1

The normal cron doesn't give you that level of expressiveness but there's nothing stopping you from putting further restrictions in the command portion of the entry:

*/3 8-15 * * * [[ 1$(date +\%H\%M) -ge 10830 ]] && [[ 1$(date +\%H\%M) -le 11515 ]] && payload

This will actually run the cron job itself every three minutes between 8am and 4pm, but the payload (your script that does the actual work) will only be called if the current time is between 8:30am and 3:15pm.

The placing of 1 in front of the time is simply a trick to avoid issues treating numbers starting with zero as octal.

---

In fact, I have a script withinTime.sh that proves useful for this sort of thing:

usage() {
    [[ -n "$1" ]] && echo "$1"
    echo "Usage: withinTime <hhmmStart> <hhmmEnd>"
}

validTime() {
    [[ "$1" =~ ^[0-9]{4}$ ]] || return 1  # Ensure 0000-9999.
    [[ $1 -le 2359 ]] || return 1         # Ensure 0000-2359.
    return 0
}

# Parameter checking.

[[ $# -ne 2 ]] && { usage "ERROR: Not enough parameters"; exit 1; }
validTime "$1" || { usage "ERROR: invalid hhmmStart '$1'"; exit 1; }
validTime "$2" || { usage "ERROR: invalid hhmmEnd '$2'"; exit 1; }

now="1$(date +%H%M)"
[[ ${now} -lt 1${1} ]] && exit 1  # If before start.
[[ ${now} -gt 1${2} ]] && exit 1  # If after end.

# Within range, flag okay.
exit 0

With this script in your path, you can simplify the cron command a little:

*/3 8-15 * * * /home/pax/bin/withinTime.sh 0830 1515 && payload