$re = '/^(000[1-9]|00[1-9]\d|0[1-9]\d\d|100\d|10[1-9]\d|1[1-9]\d{2}|[2-9]\d{3}|[1-9]\d{4}|1\d{5}|2[0-6]\d{4}|27[0-4]\d{3}|275[0-6]\d{2}|2757[0-5]\d|275760)-W(([1-4]\d)|(5[0-3])|0[1-9])$/m';
$str = 'min possible year :
0001-W10
max possible year :
275760-W05
min possible week :
1969-W01
max possible week :
1969-W53
';
$subst = "$1-W$2";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php