Automation

I'm trying to get the value of a set policer depending on what encapsulation is set on a unit.  Since family inet has not encapsulation set, I've used the if clause below to set family to 'inet' if no encapsulation is set.  This works well.

        var $family = {
           if ($top/interfaces/interface[name == $phyifname]/unit[name == $unit]/encapsulation) {
             expr $top/interfaces/interface[name == $phyifname]/unit[name == $unit]/encapsulation;
           } else {
             expr "inet";
           }
        }
        var $policer_in = $top/interfaces/interface[name == $phyifname]/unit[name == $unit]/family[name == $family]/policer/input;
        var $policer_out = $top/interfaces/interface[name == $phyifname]/unit[name == $unit]/family[name == $family]/policer/output;

The problem comes in the last two lines.  The 'family[name == $family]' doesn't work as I'd expect.  I believe this is because family xxx is its own node (whats the right term for this?), as opposed to a node that expects an argument (ie, name in slax)

Can someone set me in the right direction on this?

You can check the name of the context node by using the name() function.

So something like this might be what you are looking for:

var $policer_in = $top/interfaces/interface[name == $phyifname]/unit[name == $unit]/family/*[name() == $family]/policer/input;

That worked nicely.  What is the * for before [name()... ?

* is the wildcard that matches all nodes for the given axis.  The default axis is child, so the * in that location path matches all child nodes of <family> and then the predicate [ ] narrows them down to only child nodes with the same name as the $family variable.