How can substr() function be used in PHP to calculate the position to delete based on the length of the string and the known portion to be deleted?

When using the substr() function in PHP to delete a portion of a string, you need to calculate the position to delete based on the length of the string and the known portion to be deleted. To do this, you can use the strpos() function to find the position of the known portion within the string, and then use that position along with the length of the known portion to determine the starting point for deletion in the substr() function.

$string = "Hello, World!";
$portion_to_delete = "Hello, ";
$position_to_delete = strpos($string, $portion_to_delete);
$length_of_portion = strlen($portion_to_delete);

if ($position_to_delete !== false) {
    $new_string = substr($string, 0, $position_to_delete) . substr($string, $position_to_delete + $length_of_portion);
    echo $new_string; // Output: World!
} else {
    echo "Portion to delete not found in string.";
}