.htaccess
    RewriteEngine On
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule ^(.*)$ $1.php [L,QSA]
    # http://domain/about -> http://domain/about.php
     
    --------------------------------------------------
     
    .htaccess
    RewriteEngine On
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule ^(.*)$ index.php?q=$1 [L,QSA]
    # http://domain/about -> http://domain/index.php?q=about
     
    <?php
	function string_to_underscore_name($string) {
$string = preg_replace('/[\'"]/', '', $string);
$string = preg_replace('/[^a-zA-Z0-9]+/', '_', $string);
$string = strtolower(trim($string, '_'));
return $string;
}
echo string_to_underscore_name("13: inside movie films```''''---\//\Bye!?");
//Output: 13_inside_movie_films_bye

    // $url_data is an array
    $url_data = explode("/",$HTTP_SERVER_VARS['PATH_INFO']);
    ?>