How to tell if a user is logged in?

[tabor.carlton]

If the user is logged in, I'd like to show a 'view cart' link instead of a 'sign in/register' link.

Is there a reference anywhere to global variables, or a convenient snippet I can drop in?

I'm hoping it's something like:

if ($user_logged_in) {.... or something similar

Thanks

[DrByte]

There's an example of that already in the default tpl_header.php: The login link turns to a logout link if the customer is already logged in. And the "shopping cart" and "checkout" links appear if something is in the cart.

[tabor.carlton]

Thanks Dr. Byte,

I'd overlooked that as I'd customized that page a lot and ripped a lot of code out.

here it is for other people's sake (just testing a session):

<?php if ($_SESSION['customer_id']) { 
          $content .= 'logged in content here';
  } else { 
          $content .= 'logged out content here';
  } ?>