What is the best way to determine which variable was passed when multiple variables can be passed in PHP?

When multiple variables can be passed in PHP, the best way to determine which variable was passed is to use the `isset()` function to check if a variable has been set. You can then use conditional statements to determine which variable was passed based on the result of the `isset()` function.

if(isset($_POST['variable1'])){
    // Variable 1 was passed
    $variable = $_POST['variable1'];
} elseif(isset($_POST['variable2'])){
    // Variable 2 was passed
    $variable = $_POST['variable2'];
} else {
    // Handle case when no variable was passed
    $variable = "No variable passed";
}

echo $variable;