Allow only [a-z][A-Z][0-9] in string using PHP

Question

How can I get a string that only contains a to z, A to Z, 0 to 9 and some symbols?

Answer 1

Both these regexes should do it:

$str = preg_replace('~[^a-z0-9]+~i', '', $str);

Or:

$str = preg_replace('~[^a-zA-Z0-9]+~', '', $str);