php simplexml_load_file

I'm new to PHP and this may be a stupid question to ask, so don't vote me down just because I don't understand something...

php -r "print_r(simplexml_load_file('http://twitter.com/statuses/user_timeline/31139114.rss'));"

let's take this for an example, by running this command i get (on screen) XML output.

my question is it possible to save this data instead of just screen but in a file and then read that file and have exact same as if you've have made that simplexml_load_file()

You can download the data, using something like file_get_contents ; it'll get you the whole XML in a single PHP string.
For instance :

$xml = file_get_contents('http://twitter.com/statuses/user_timeline/31139114.rss');

$xml now contains the XML string.

Then, you can write that string to a file, using file_put_contents.
For instance :

file_put_contents('/home/squale/developpement/tests/temp/test.xml', $xml);

And, to check the file, from the command-line :

$ cat test.xml                                                                                                                                                                                                   
<?xml version="1.0" encoding="UTF-8"?>                                                                                                                                                                           
<rss xmlns:atom="http://www.w3.org/2005/Atom" version="2.0">                                                                                                                                                     
  <channel>                                                                                                                                                                                                      
    <title>Twitter / eBayDailyDeals</title>                                                                                                                                                                      
    <link>http://twitter.com/eBayDailyDeals</link>                                                                                                                                                               
    <atom:link type="application/rss+xml" href="http://twitter.com/statuses/user_timeline/31139114.rss" rel="self"/>                                                                                             
    <description>Twitter updates from eBay Daily Deals / eBayDailyDeals.</description>                                                                                                                           
    <language>en-us</language>                                                                                                                                                                                   
    <ttl>40</ttl>                                                                                                                                                                                                
    <item> 
...
...

After that, you can use simplexml_load_file to read from that file.
For instance :

$data = file_get_contents('/home/squale/developpement/tests/temp/test.xml');

And $data now contains your XML string ;-)

Considering the XML you get from the remote server is a string, no need to serialize it ; and file_put_contents is easier that fopen+fwrite+fclose ;-)