How to execute script on schedule?

Question

I have two Python scripts on my machine that I want to execute two times a day on specific time period. How do I automate this task? Since I will be away from home and thus my computer for a while, I want to upload them to a site and be executed from there automatic without me doing anything.

How can I do this?

Answer 1

You can use cron for this if you are on a Linux machine. Cron is a system daemon used to execute specific tasks at specific times.

cron works on the principle of crontab, a text file with a list of commands to be run at specified times. It follows a specific format, which can is explained in detail in man 5 crontab

Format for crontab

Each of the sections is separated by a space, with the final section having one or more spaces in it. No spaces are allowed within Sections 1-5, only between them. Sections 1-5 are used to indicate when and how often you want the task to be executed. This is how a cron job is laid out:

minute (0-59), hour (0-23, 0 = midnight), day (1-31), month (1-12), weekday (0-6, 0 = Sunday), command

01 04 1 1 1 /usr/bin/somedirectory/somecommand

The above example will run /usr/bin/somedirectory/somecommand at 4:01am on January 1st plus every Monday in January. An asterisk (*) can be used so that every instance (every hour, every weekday, every month, etc.) of a time period is used. Code:

01 04 * * * /usr/bin/somedirectory/somecommand

The above example will run /usr/bin/somedirectory/somecommand at 4:01am on every day of every month.

Comma-separated values can be used to run more than one instance of a particular command within a time period. Dash-separated values can be used to run a command continuously. Code:

01,31 04,05 1-15 1,6 * /usr/bin/somedirectory/somecommand

The above example will run /usr/bin/somedirectory/somecommand at 01 and 31 past the hours of 4:00am and 5:00am on the 1st through the 15th of every January and June.

The "/usr/bin/somedirectory/somecommand" text in the above examples indicates the task which will be run at the specified times. It is recommended that you use the full path to the desired commands as shown in the above examples. Enter which somecommand in the terminal to find the full path to somecommand. The crontab will begin running as soon as it is properly edited and saved.

You may want to run a script some number of times per time unit. For example if you want to run it every 10 minutes use the following crontab entry (runs on minutes divisible by 10: 0, 10, 20, 30, etc.)

*/10 * * * * /usr/bin/somedirectory/somecommand

which is also equivalent to the more cumbersome

0,10,20,30,40,50 * * * * /usr/bin/somedirectory/somecommand