Run Cron Job every 45 minutes with Node-Cron

I'm more familiar with cron than with node-cron, but I've taken a quick look at the documentation.

If I understand it correctly, node-cron uses a syntax similar to that used by cron, but with an additional "seconds" field. So where a cron job might have:

# min hour mday month wday command
*/15  *    *    *     *    some-command

to schedule some-command to run every 15 minutes, node-cron would use a similar syntax to specify the time to run:

'0 */15 * * * *'

(with an additional field to specify seconds), but it executes a specified JavaScript function, not an external command.

In standard cron, there is no syntax to specify running a job every 45 minutes. A specification of 0/45 * * * * would run a job twice each hour, at 0 and 45 minutes after the hour. To run a job every 45 minutes (at 00:00, 00:45, 01:30, 02:15, ..., i.e., 32 times per day) you'd have to schedule it to run every 15 minutes, and then invoke a script that checks the current time to decide whether to do anything.

Or you can write an exhaustive list of all the times you want the job to run:

 0  0 * * * some-command
45  0 * * * some_command
30  1 * * * some_command
15  2 * * * some_command
# 28 lines omitted

I'd definitely want to write a script to generate this list.

(This is workable because 24 hours happens to be a multiple of 45 minutes. You couldn't run something every 35 minutes this way.)

A similar approach should work for node-cron. Schedule the function to run every 15 minutes, and invoke a function that checks the current time to decide whether to run. For example, you can check whether the number of minutes since midnight modulo 45 is zero. (You might want to allow for a small variance in case the scheduling is not exact.)

I don't know JavaScript well enough to suggest the best way to write this function, but it should be reasonably straightforward.

Or write 32 lines to specify all the times you want it to run.

You're probably looking for

0 */45 * * * *

The ranges are here.

• Seconds: 0-59
• Minutes: 0-59
• Hours: 0-23
• Day of Month: 1-31
• Months: 0-11
• Day of Week: 0-6

There is no direct way to do this. However, we can get the result by intercepting the schedule using a shell command within the target script.

First, run the script at every 15 minutes:

*/15 * * * * <target_script>

Then, within the target_script, place the following code before actual codes:

#!/bin/sh

# Exit except at 0:45, 1:30, 2:15, 3:00, 3:45 etc

if ! echo "((`date +%-H`*60)+`date +%-M`)/45" | bc -l | grep "\.0*$" &> /dev/null;
then exit 1;
fi

# Your actual code goes here;

I tried this string for a 45-second interval and it works well:

'*/45 * * * * *'