How can the use of file_exists() and fopen() functions in PHP scripts impact the overall functionality and security of the application?

Using file_exists() and fopen() functions in PHP scripts can impact the overall functionality and security of the application if not used carefully. These functions can potentially allow an attacker to access sensitive files on the server or manipulate file operations. To mitigate these risks, it is crucial to validate user input, sanitize file paths, and implement proper error handling.

// Example of secure usage of file_exists() and fopen() functions
$file_path = 'path/to/file.txt';

if (file_exists($file_path)) {
    $file = fopen($file_path, 'r');
    // Perform operations on the file
    fclose($file);
} else {
    echo 'File does not exist.';
}