Remove a part of a string, but only when it is at the end of the string

Question

I need to remove a substring of a string, but only when it is at the END of the string.

for example, removing \'string\' at the end of the following strings :

Answer 1

Using regexp may fails if the substring has special characters.

The following will work with any strings:

$substring = 'string';
$str = "this string is a test string";
if (substr($str,-strlen($substring))===$substring) $str = substr($str, 0, strlen($str)-strlen($substring));