callback

$content = file_get_contents('http://www.example.com/');
if (strpos( $content, 'строка' ) !== false) {
// тут делаешь что то 
}

server {
    listen 80;
    server_name sub.site.ru;
    return 301 $scheme://site2.ru$request_uri;
}

Mozilla/5.0 (iPhone; CPU iPhone OS 6_1_3 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/6.0 Mobile/10B329 Safari/8536.25

Mozilla/5.0 (iPad; CPU OS 6_1_3 like Mac OS X) AppleWebKit/536.26 (KHTML, like Gecko) Version/6.0 Mobile/10B329 Safari/8536.25

$(function(){

    $(document.body).on('keydown', 'textarea', function(e){
        if (e.keyCode == 9) e.preventDefault();
        /* do something */
    })

});