ibragimof on "Edit the header.php"

I can not edit the file header.php in wp-content\themes\my
my code

$url = 'http://...........';
$start = '<div class="marquee">';
$finish = '<div class="row-fluid" id="content">';
function parser($url,$start,$finish) {
    $content = file_get_contents($url);
    $position1 = strpos($content, $start);
    $position2 = strpos($content, $finish);
    $content = substr($content, $position1, $position2-$position1);
    $content = $content;
    echo ($content);
    return $content;
}

parser($url, $start, $finish);

if i put this code to header.php, my site don't work