Does your hosting company give you access to you can create
your personal crontab? If not, you're SOL.
Do you have PHP compiled as a CGI or as mod_php? If the latter,
you're going to need some command-line way to request a page
one your server so that the php script can do its thing: wget,
curl, or even lynx will work here. (It goes without saying that
you don't care about the html output from such a script--
nor can it be interactive in any way.!)
The crontab itself is quite simple. It contains one line per command
formatted as follows:
minute hour day month day-of-week command [args...]
For example, on a system I worked on there's a cleanup process that
runs every hour at 20 minutes past the hour:
20 nobody /usr/local/bin/reaper
What happens is the cron daemon wakes up every minute and
inspects the list of tasks. If the current minute, hour, date,
month, and day-of-week match, the program is run. (The star
is a wildcard that will match any value.) Thus, the program
runs every hour at 20 past.
