What is a common method for automating the execution of a PHP script once a day?

To automate the execution of a PHP script once a day, a common method is to use a cron job. A cron job is a time-based job scheduler in Unix-like operating systems that can be used to schedule tasks to run at specific intervals.

```php
// Sample PHP script to be executed once a day
<?php

// Your PHP script code here

?>

```

To schedule this script to run once a day using a cron job, you can add the following command to your crontab file:

```bash
0 0 * * * php /path/to/your/script.php
```

This cron job will run the script at midnight (00:00) every day. Make sure to replace `/path/to/your/script.php` with the actual path to your PHP script file.