I have shared hosting and they haven't given me command line (or ssh or shell) access. Is there a way that I can run something from the command line?
Your shared hosting may give you access to cron jobs. (On cPanel hosting this may be under Advanced Tools.) Cron is a Unix command which runs a task at a specified time. You can create a cron job to run the task you want, if your shared hosting lets you.
cPanel gives this warning though:
You need to have knowledge of *nix commands before you can use cron jobs effectively. Check your script with your hosting administrator before adding a cron job.