How can PHP be used to detect and handle unwanted content in a string, such as excessive line breaks?

Excessive line breaks in a string can be detected and handled in PHP by using regular expressions to search for patterns of consecutive line breaks and then replacing them with a single line break. This can help clean up the string and make it more readable.

$string = "This is a string\n\n\n\nwith excessive line breaks\n\n\n\n\n\n\n\n\n";
$cleaned_string = preg_replace("/\n{3,}/", "\n\n", $string);
echo $cleaned_string;