What are the differences in behavior between including files using absolute paths versus relative paths in PHP?

When including files in PHP, using absolute paths means specifying the full path from the server's root directory, while relative paths are specified in relation to the current working directory. Absolute paths are more reliable and less prone to errors, especially when including files from different directories or when moving files around. Relative paths are more flexible and easier to work with within the same directory structure.

// Including a file using an absolute path
include_once('/var/www/html/includes/config.php');

// Including a file using a relative path
include_once('includes/config.php');