*> sudo visudo

#find 'root ALL(...' and append this line below:

www-data ALL=NOPASSWD:/usr/local/bin/myscript.sh

#Save

*> sudo cp myscript.sh /usr/local/bin/
*> sudo chmod 777 /usr/local/bin/myscript.sh

#at php script:

<?php

$cmd = shell_exec("/usr/local/bin/myscript.sh params");
echo $cmd;

?>