Opening a file or a url in the same script

[Kelly]

I wrote this script to work on local files is there a way I can change
something here so
that I can add a url and run that through the script aswell?
---------------------------------------------------------------------
<form action="<?= $PHP_SELF ?>" method="POST">
URL: <input type="text" name="url" value="<?= $url ?>"/><br>
<input type="submit">
</form>

// this is after the form is posted
$remote = fopen($url, 'r');
$html = fread($remote, 1048576);
fclose($remote);
---------------------------------------------------------------------

The script is working I just want to add this functionality but I don't even
know how to go about looking something like this up. It seems to work
once in awhile but not consistently and I think it is the way it is opening
the webpage. If I copy the same page and run it on my machine as a local
file it always works.
Thanks,
Kelly