Not delete the text, but show it?

[akiznin]

How can I make it so instead of deleting anything that starts with a number from 0-9, I want it to only show things that start with a number from 0-9, how could i do this?

 

<?php
$fn = "1.txt";
$file = file_get_contents($fn);
$file = preg_replace('/[0-9]/','',$file);
echo $file;
?>

[JasonLewis]

What about using preg_match instead, or replaying anything that isn't a number.