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File: Cron_parser_documentation.txt

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File: Cron_parser_documentation.txt
Role: Documentation
Content type: text/plain
Description: Documentation on intended usage
Class: PHP Cron
Parse cron schedules to find when cron job ran
Author: By
Last change:
Date: 18 years ago
Size: 2,743 bytes
 

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PHP Cron parser documentation ============================= This is some rudimentary documentation to explain the purpose and intended use of the Cron Parser class. Currently, the class exists in isolation, but when Iíve worked more on an implementation, Iíll post concrete examples and perhaps a complete cron replacement system. This class does *not* read in your crontab. It relies on being told a schedule from a crontab and parsing that. A typical implementation would be to use a database to store data about cron jobs. Typically, in a two-server environment, serverB's crons would be set to run 2 minutes after serverA's crons were due to run, first checking if the cron on serverA actually ran, thus providing cron redundancy. Current functionality _____________________ The class has various internal methods, but it is not intended that these be invoked. Instead, just one method should be used, as follows: $cron_schedule = "0 5 * * *";//example schedule, (5am each day) //Constructor - takes cron schedule as an argument $cron = new CronParser($cron_schedule); //getLastRan method - returns array (0=minute, 1=hour, 2=dayOfMonth, 3=month, 4=week, 5=year) $lastRan = $cron->getLastRan(); //Make a timestamp from the array $cron_ran = mktime ( $lastRan[1] ,$lastRan[0],0 , $lastRan[3] ,$lastRan[2], $lastRan[5]); So, in this example, itís obvious that the last ran time was 5am on the current day. However, this calculation becomes more complex when some other cron schedules are involved, like: $cron_schedule = "0,12,30-35 5,7-9 * 9-12 0-3,6"; This example asks cron to run a program at a variety of different times, and the last ran time might be last yesterday, last week, last month, or even last year. So, if you need to know if a cron ran, you can add logging to your app, and then create a CronParser instance to determine when the cron job was due to run last and use fuzzy time comparison between that time and the timestamp of your log entry in your database. Using this system, you can add an environment variable to your crontab like (HOSTNAME="serverA") and use this in your logging to determine which server ran the cron. Use logic to run the cron on serverB if serverA failed to log success. Future expansion of this project ________________________________ The basic parsing of cron schedules has been cracked, and thereís no reason why a whole host of PHP applications to control scheduled execution of scripts canít be created, for sysadmin and web management use. I plan to write some apps that I can release under GPL / LGPL for these purposes. Mick Sear (http://www.ecreate.co.uk, mick@ecreate.co.uk)