Should PHP developers always escape variables, regardless of their source, to prevent potential security vulnerabilities in their code?

It is best practice for PHP developers to always escape variables to prevent potential security vulnerabilities such as SQL injection attacks. By escaping variables, developers can ensure that any user input is sanitized before being used in database queries or other sensitive operations. This helps to protect against malicious input that could potentially exploit vulnerabilities in the code.

// Example of escaping variables to prevent SQL injection
$unsafe_variable = $_POST['user_input'];
$safe_variable = mysqli_real_escape_string($connection, $unsafe_variable);

// Now use $safe_variable in your SQL query
$query = "SELECT * FROM users WHERE username = '$safe_variable'";
$result = mysqli_query($connection, $query);