Question

I have a fairly light script that I want to run periodically in the background every 5 hours or so. The script runs through a few different websites, scans them for new material, and either grabs .mp3 files from them or likes songs on youtube based on their content. There are a few things I want to achieve with this program that I am unsure of how to attain:

• Have the program run every 5 hours — I’m not to familiar with system-level timing operations.
• Have the program efficiently run in the background — I want these ‘updates’ to occur without the user knowing.
• Have the program activate on startup — I know how I would set this up as a user, but I’m not sure how to add such a configuration to the python file, if that’s even possible. Keep in mind that this is going to be a simple .py script — I’m not compiling it into an executable.

The program is designed mainly with OSX and other Unix based systems in mind. Any advice on achieving some of these goals?

Answer 1

If your script doesn’t need to be constantly in execution, and it sounds like it doesn’t, I’d suggest you set up a cron job.

On a typical Linux box, you can edit your crontab file via:

$ crontab -e

This will open your crontab in your standard editor and install the crontab file for you after you’re done (i.e. you save it)

A typical crontab command looks like:

# m h  dom mon dow   command
 15  0   *   *   *    /bin/bash /home/yourself/bin/dump_my_tables.sh

this line will execute dump_my_tables.sh every day at 00:15. Your script will need a like like the following:

0  */5  *  *  *   /usr/bin/python /home/yourself/bin/scrape_the_web.py

nb:

• Time is the machine’s local time (!)
• Some cron versions don’t accept */5 syntax, you have to manually specify the hours when you want the script to be scheduled, i.e. 0,5,10,15,20
• You might want to redirect output, but it’s out of this answers’ scope