[Anseur]

I think your looking for something like this:

PHP Code:


if ($_REQUEST['do'] == 'blah')
{
some code here
} 


In this case 'some code here' gets run if you visit the PHP file in question with somefile.php?&do=blah in the URL.

In the case of your example above it might look something more like

PHP Code:


<form>
Username:
<input type="text" name="Username" 

if ($_REQUEST['u'] != '' )
{ 
value="$_REQUEST['u']"
}
/>

</form> 


This would put the user id into the username box, not the username, but it should give you an idea of the general method.

(untested)

However, using superglobals like this is a really bad idea, because it would allow someone to inject code into the php file by the address bar. At the very least you should attempt to sanitize the input before using it. (with regex maybe?)

There may be a safer or better way of doing this, but I'll leave that reply to someone more experienced than myself at PHP.