Retrieving and writing a file to system

What's the simplest 开发者_开发问答way in PHP, to:

1. Retrieve a file from an external URL (http://test.com/thisfile)?

2. If successful, delete local file /root/xml/test.xml.

3. Rename downloaded file to test.xml.

4. Write new file to /root/xml/ folder.

This will be a private script, so security or error handling are not important concerns.

---

$contents = file_get_contents( 'http://test.com/testfile' );
if( $contents ) {
     $file = '/root/xml/test.xml';
     unlink( $file );
     file_put_contents( $contents, $file ); 
}

---

Assuming correct configuration,

$file = file_get_contents('http://test.com/thisfile');
if($file) {
    unlink('/root/xml/test.xml');
    file_put_contents('/root/xml/test.xml');
}

Or something along those lines.