Search Engine using "if..else" statements

I’m making a site with more than one artist on it.
I want to make an extremely simple search.

When they for example enter “nas” in the search box.

the php header will automatically redirect it to a page called “nas.php”.

I know it can be done using if else. like for example.

<?
If ( $textbox == “nas” || “nasir” )
{
header(‘location: nas.php’);
}
else {
echo “not found”
}
?>

Please help me by writing the code. I’ve completely forgotten PHP.
Thanks. Hope you guys can help!