Is one regular expression enough?

Question

PHP

Here is a regular expression, it removes everything except from a to z.

$url_path = preg_replace('/[^a-z]/', '', $url_path);

Examples of disputing the use of only such a method without

strip_tags($_GET['input_text']); 
$input_text = htmlspecialchars($input_text); 
$input_text = mysql_escape_string

I did not find. Can this method cause a vulnerability?

Answer 1

For URL: No. Can not.
And then - it all depends on the script code (for example, a router), which can open access even with a normal URL request.

Answer 2

Instead of such a collective farm, use better parameterized mysqli or PDO queries. It is high time to abandon mysql_, these functions have been deprecated for two years now.