If you must do this in one line, IMO it is preferable to use list
:
list(, $x) = explode('/', $path);
This is arguably better than the long-winded
$x = implode('', array_slice(explode('/', $path), 1, 1));
in which it's easy to forget what you were supposed to be doing in the first place.
If you are not sure if there will be a second element, you can guard against problems with
list(, $x) = array_pad(explode('/', $path), 2, null);
However, I don't really recommend any of the above for real code. Use the two-liner if you have to; it will still be easier to read than any of these solutions.