How to declare a global variable in php?

I have code something like this:

<?
    $a="localhost";
    function body(){
        global $a;
        echo $a;
    }

    function head(){
        global $a;
        echo $a;
    }

    function footer(){
        global $a;
        echo $a;
    }
?>

is there any way to define the global variable in one place and make the variable $a accessible in all the functions at once? without making use of global $a; more?