When using preg_replace I get double characters...?

Question

When I use the following script, I get double characters. Why?

$clean_lastname = "Dür";
$clean_lastname = preg_replace("/[ùúûü]/", "u", $clean_lastname);
echo $clean_lastname;

Output: Duur

I want it to be Dur.

I am still doing something wrong... What's up with the 'putting one value of an array in the preg function?

$clean_lastname = "Boerée";
$l = 0;
$pattern = array('[ÀÁÂÃÄÅ]','[Ç]','[ÈÉÊË]','[ÌÍÎÏ]','[Ñ]','[ÒÓÔÕÖØ]','[Ý]','[ß]','[àáâãäå]','[ç]','[èéêë]','[ìíîï]','[ñ]','[òóôõöø]','[ùúûü]','[ýÿ]');
$replace = array(A,C,E,I,N,O,Y,S,a,c,e,i,n,o,u,y);

foreach ($pattern as $wierdchar)
{
    $clean_lastname = preg_replace('/$wierdchar/u', '$replace[$l]', $clean_lastname);
    $l++;
}

//$clean_lastname = preg_replace('/[èéêë]/u', 'e', $clean_lastname);

//$clean_lastname = strtr($clean_lastname, "ùúûü","uuuu");
echo $clean_lastname;

Answer 1

$clean_lastname = str_replace(array('ù', 'ú', 'û', 'ü', 'Ù', 'Ú', 'Û', 'Ü'), array('u', 'u', 'u', 'u', 'U', 'U', 'U', 'U'), $clean_lastname);

// OR to solve your initial issue:

$clean_lastname = preg_replace('/[ùúûü]/u', 'u', $clean_lastname);