What are some best practices for handling undefined variables in PHP scripts?

When handling undefined variables in PHP scripts, it is best practice to check if a variable is set using the isset() function before trying to access its value. This helps prevent PHP from throwing notices or warnings when an undefined variable is accessed. Additionally, using the null coalescing operator (??) can provide a default value if the variable is undefined.

// Check if the variable is set before accessing its value
if (isset($variable)) {
    // Use the variable if it is set
    echo $variable;
} else {
    // Provide a default value if the variable is undefined
    $variable = "default value";
    echo $variable;
}