In what ways can PHP beginners improve their understanding of file handling and security in PHP scripts?

Beginners can improve their understanding of file handling and security in PHP scripts by familiarizing themselves with functions like fopen, fwrite, and fclose for file handling, and by implementing proper input validation and sanitization techniques to prevent common security vulnerabilities like SQL injection and cross-site scripting attacks. 

// Example of input validation to prevent SQL injection
$username = $_POST['username'];
$password = $_POST['password'];

// Sanitize input
$username = mysqli_real_escape_string($conn, $username);
$password = mysqli_real_escape_string($conn, $password);

// Perform query
$query = "SELECT * FROM users WHERE username='$username' AND password='$password'";
$result = mysqli_query($conn, $query);

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