CODEWITHSUNDEEP
bashjob-scheduling
user2726921
user2726921

Reputation: 53

Run variable length bash script at the top of the hour without cron

I have a simple bash script that runs some tasks which can take varying amounts of time to complete (from 15 mins to 5 hours). The script loops using a for loop, so that I can run it an arbitrary number of times, normally back-to-back.

However, I have been requested to have each iteration of the script start at the top of the hour. Normally, I would use cron and kick it off that way, every hour, but since the runtime of the script is highly variable, that becomes trickier.

It is not allowable for multiple instances of the script to be running at once.

So, I'd like to include the logic to wait for 'top of the hour' within the script, but I'm not sure of the best way to do that, or if there's some way to (ab)use 'at' or something more elegant like that. Any ideas?

Upvotes: 0

Views: 205

Answers (1)

that other guy
that other guy

Reputation: 123570

You can still use cron. Just make your script use a lock file. With the flock utility you can do:

#!/bin/bash
exec 42> /tmp/myscriptname.lock
flock -n 42 || { echo "Previous instance still running"; exit 1; }

rest of your script here

Now, simply schedule your job every hour in cron, and the new instance will simply exit if the old one's still running. There is no need to clean up any lock files.

Upvotes: 2

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