How can PHP developers ensure that their code is portable and functions correctly across different servers, especially in terms of file permissions and ownership?

PHP developers can ensure their code is portable and functions correctly across different servers by using relative paths instead of absolute paths for file operations, checking and setting file permissions using PHP functions like `chmod()`, and using appropriate error handling to address any permission-related issues that may arise. Additionally, developers can use server-agnostic functions and avoid hardcoding server-specific configurations.

// Example of setting file permissions using PHP's chmod() function
$filename = 'example.txt';
$permissions = 0644; // Set read and write permissions for owner, read permissions for group and others
if (file_exists($filename)) {
    chmod($filename, $permissions);
} else {
    echo "File does not exist.";
}