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In this tutorial, we will show you a few useful examples on how to create a cron job for your script-based websites. Scripts usually include a working environment sophisticated enough to work as a multi-structural base for performing a wide variety of tasks which altogether are easily implemented and combined into forums, informational portals, blogs, billing management systems, etc. Although most often the implementation of a given script is done in real time and the users operate with a web driven GUI to navigate through what the given script might offer, there are still some 'assignable' tasks that only site administrators can schedule. Those tasks are what we call cron jobs - they carry important site/script maintenance information and pass system commands to the Cron Daemon via Crontab. Cron jobs are scheduled to execute shell commands or scripts at a given time or date. Below you will find a few examples representing a shell command execution cron job and a script (cgi / php) execution cron job. Cron jobs have the following formatting that we will divide into groups:
Cron job time schedule - [ Minute - Hour - Day - Month - Weekday ]
Cron job shell command - [ARGUMENTS]
Cron job script command - [PATH OF PHP/PERL] [ARGUMENTS] [PATH OF PHP SCRIPT]
Here is an example of cron job time scheduling and the allowed cron job operators:
.---------------- minute (0 - 59) | .------------- hour (0 - 23) | | .---------- day of month (1 - 31) | | | .------- month (1 - 12) OR jan,feb,mar,apr ... | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat | | | | | * * * * * command to be executed * * * * * => Execute every minute 0 * * * * => Execute every Hour 0 0 * * * => Execute every midnight 0 0 0 * * => Execute every Month 0 0 0 0 * => Execute every Weekdays
You can create cron jobs via your Web Hosting Control Panel. Simply navigate to Site Management > Crontab. In this section of the Control Panel you can see the cron jobs already created and you can also add new ones. To set up a cron job you must specify the e-mail address where the results will be sent to, the date and the time when the job should be executed and the command, which should be executed.
Here is an example of running shell command driven cron jobs and script execution cron jobs:0 * * * * rm -f * /home/www/my-best-domain.com/temp/
This command will initiate the rm (remove / delete) utility for file/folder deletion and will forcibly delete all the files under /home/www/my-best-domain.com/temp/
Let us say that you want to mail newsletters, site updates, etc. to your clients on a daily basis. Most script systems already have prebuilt scripts for this purpose and many more automated services. The cron job would look like this:0 0 0 0 * /usr/bin/php /home/www/my-best-domain.com/mailcron.php
There are also several useful additions to cron jobs, such as, for example, MAILTOemail@example.com, which will send you the output of the cron job, which in many cases is a very useful option, especially when your cron job is not working according to plan and produces errors. With the mailed output you will be surely able to debug the issue. Such a cron job would look like this:0 0 0 0 * /usr/bin/php /home/www/my-best-domain.com/mailcron.php MAILTOfirstname.lastname@example.org
You can learn more on the allowed file types when using Crontab in the following tutorial: Files that could be executed with crontab - allowed file extensions.