PHP and MySQL®: Create-Modify-Reuse

3.5. Setting Up the Mailing List

The project scripts in this chapter aren't meant to be run by a user visiting a web page, but rather periodically scheduled and executed automatically by the system. The digest.php script should run once a day to send the daily digest message, probably sometime late at night or during early morning. The best way to schedule individual.php depends on the membership size and the amount of messages your list will be receiving. Exactly how scheduling is accomplished depends on which operating system is installed on the server.

On servers running a unix-variant operating system, you'll be adding entries to a crontab file to schedule their runs and the cron daemon will execute them when it's time. To add entries to your crontab file, call crontab -e from the command line.

Each entry in the crontab file is made up of a series of fields separated by a space. Normally there are seven fields per entry, and each entry is on its own line. An asterisk (*) may be used in any field with no specified value and some versions of cron allow you to specify multiple values for a field by separating them with a comma.

Table 3-2 shows the expected fields.

Table 3-2. crontab File Fields

Field	Description
Minute	What minute (0 through 59) the command will run
Hour	Hour of the day in 24-hour format (0 through 23 with 0 as midnight)
Date	Day of the month (0 through 31)
Month	Month, may either be numeric (0 through 12) or textual ( January through December)
Day	Day of the week, may either ...