I want to get one php script from one site,how can I get it?is there any program that gets the site including PHP files?
Is it just PHP or does it use a database such as MySQL also? Also what type of control panel do you have? cPanel? You should be able to backup your hosting account via a backup feature, then upload that backup to your new host and restore - transfer complete.
if it's not your site the only way would be to contact the owner and make him offer for the script. You might get lucky. PHP files can't be downloaded using a browser (not unless you hack the website).
PHP scripts are interpretted server side before being presented to the client and hence you can not see their contents without server access such as FTP/SSH.