Regular Expression to Escape all Illegal (non alphanumeric) Characters Except a space

I created the following functions which I found to be the easiest way to escape all illegal characters.


To escape all illegal (non alphanumeric) characters except a white space.

<?php
function stripChars($string) {
$new_string=trim(ereg_replace("[^a-zA-Z0-9[:space:]]", "", $string));
return $new_string;
}

$result=stripChars("This !is__  a@  test&")
echo $result;
?>

The above would display "This is a test"

To Escape All characters except alphanumeric and an underscore
ereg_replace("[^a-zA-Z0-9_]", "", $string));

To Escape All characters except alphanumeric and an underscore and a dot (period)
ereg_replace("[^a-zA-Z0-9_.]", "", $string));


To Escape All characters except numeric and an underscore and a dot (period)
ereg_replace("[^0-9_.]", "", $string));