Question

I need a regex to recognize only two options, they are ‘F’ and ‘M’ chars. I am trying:

preg_replace('/([^FM]){1}/', '', $_GET['option'])

But if i type ‘MF’ it returns ‘MF’, but i am expecting ‘M’.

Can anybody help me?

Answer 1

$output = preg_replace('/^[^FM]*([FM])?.*/s', '$1', $_GET['option']);

Start at the beginning of the string. Consume all non-FM characters. Then match one F or M character (if there is one). Match the rest of the input. Replace with the matched character. Note that you will end up with an empty string if there was no M or F at all.

However, you should probably rethink how you get that data, since it seems to be a boolean value (but you take care of an arbitrary string that might contain the desired characters).

If you generate the value yourself (from some other website), you should be able to know that values that haven’t been tampered with are either "M" or "F". So why not just go with:

if ($_GET['option'] == "M")
    // male...
elseif ($_GET['option'] == "F")
    // female...
else
    // someone tried to mess with you ...