Thank you very much dagon and bradgrafelman.
Both of you are correct.
i enabled display_errors and error_reporting to E_ALL as bradgrafelman's suspect then saw the errors;
Warning: file() [function.file]: URL file-access is disabled in the server configuration in ...
Warning: file(http://www.site.com/test.txt) [function.file]: failed to open stream: no suitable wrapper could be found in ...
Then read the Supported Protocols and Wrappers for links to information .. as dagon's suspect,
then solved the problem by applying allow_url_fopen to be enabled at php.ini.
Now everything is Ok and print_r function worked.
Thanks again.