What are the potential memory limitations when working with multiple files in PHP, and how can they be managed?

When working with multiple files in PHP, one potential memory limitation is that loading large files or opening too many files at once can consume a significant amount of memory. To manage this, you can use techniques such as reading files line by line instead of loading the entire file into memory, closing files after use, and using memory-efficient functions like `fopen`, `fread`, and `fclose`.

$file = fopen("example.txt", "r");

if ($file) {
    while (($line = fgets($file)) !== false) {
        // Process the line here
    }
    
    fclose($file);
} else {
    echo "Error opening file.";
}