How can PHP be used to determine the total number of characters in a string for truncation purposes?

To determine the total number of characters in a string for truncation purposes in PHP, you can use the `strlen()` function to get the length of the string. This length can then be compared to a specified limit to decide whether the string needs to be truncated or not.

$string = "This is a sample string to demonstrate truncation.";
$limit = 20;

if(strlen($string) > $limit) {
    $truncated_string = substr($string, 0, $limit) . "...";
    echo $truncated_string;
} else {
    echo $string;
}