Every half hour script

[Blake121]

Hi. I have a problem that I don't know how to solve.

I need a script that will run and update some info in a DB table every half an hour.

The script itself shouldn't be to hard it's just I don't know how to make it run every half an hour.

Is there a way to make the script run without a user being there to refresh that page? Like make the server do it or something. I really can't figure out how this will work.

Thanks for your help

Blake

[ioncube]

Do you have either a dedicated server or VPS, or just a basic shared server?

[Blake121]

basic shared server i'm working on.

It supports cron jobs though. If it makes a difference at all.

[ioncube]

All the difference as in that case it should be easy. If you have access to a personal raw crontab file, simply add a line such as:

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0,30 * * * * php yourscript.php

You may need to specify a full path for the php binary and a suitable path for your script, but that's the essence of what you'd add to the crontab file. In this case it says run at 0 and 30 mins past each hour, every day, month and year. Other forms of syntax include /n to specify a repeat interval, e.g. */5, and ranges, such as 20-50 in the first field to mean every minute between 20 minutes and 50 minutes past the hour.

Without cronjobs, the trick is to hook a script into a core file of your website that gets hit on every request, record when your scheduled script was last run, and if the next trigger time has passed then execute the script as part of the page request. As long as the site gets a hit at least every minute or so then you'll get a fairly or even completely accurate scheduler that way. The slightly tricky thing with this method is that it's important to avoid race conditions in some way, such as testing that the cronjob needs running, then getting a lock (e.g. a file lock with flock()), testing again, and if it still needs running then update the time that it last ran, release the lock, and then do the work.

[Blake121]

Thanks a lot!

I'm looking into that right now

[ioncube]

You should be able to use environment variables in the crontab too, e.g.

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* * * * * $HOME/bin/somescript.sh

would run somescript.sh every minute in your account root/bin directory. This would avoid hardcoding your account directory location. You might need to ask your host or look in their KB about how to set it up though as giving the ability to run programs on a shared server is a potential security risk, and there might be limitations on what programs you can use, although you just need to run PHP cli and that should be fine.