What does a . (dot) do in PHP?

What does the following command do in PHP?

. $string   // ($string is something which i declared in the program)

Answer

On its own, that does nothing at all (it's not valid syntax). However, if you have something like this:

$string1 = "Hello ";
$string2 = "world!";
$string = $string1 . $string2;

echo $string;

?>

You will see Hello world!. The . is the string concatenation operator.