[j-nsp] Conditional statement in XPath predicates

[Jonathan Looney]

There may be a more elegant way to do this, but this seems like a place
where user-defined SLAX functions (as opposed to templates) can help, since
functions can be used in XPATH expressions.

If I recall correctly, we didn’t cover this well in the book, and I’ll take
the blame for that. They are useful and are a good tool to have in your
automation toolkit for those times when they are the right tool for the job.

However, they are covered here (among other places):
https://forums.juniper.net/t5/Automation/Scripting-How-To-Custom-functions-in-SLAX-scripts/ta-p/279074
http://libslax.readthedocs.io/en/latest/constructs.html#index-18

(Phil will probably be along soon to correct/confirm/supplement this
information.)

However, let me also say that you should generally always prefer to filter
as close to the source as possible. For example, let’s say that you were
trying to filter routes from a table with 1.4M routes. Let’s further say
that each route’s XML information was 512 bytes (which I actually suspect
might be a tad conservative). That is 700MB of data that RPD has to
generate and cscript needs to consume. If you only want a subset of those,
it would be much better to send an appropriate filter to RPD so it only
gives you the routes you want. In that case, it would probably even be
worth running a few extra cheaper RPCs (if needed) to construct the filter.

Jonathan

On Fri, Mar 9, 2018 at 7:42 AM Martin T <m4rtntns at gmail.com> wrote:

> Hi,
>
> let's say that I have a SLAX script which takes an argument named
> "interface". This "interface" can be an IFD. Is it possible to create
> an XPath statement for for-each loop, which runs for each interface if
> the "interface" is not specified and only for this one specific IFD,
> if "interface" is specified? My first idea was to do something like
> this:
>
> param $interface = "*";
>
> for-each ($result/physical-interface[name == $interface) {
>
> }
>
> This works only in case the "interface" argument is specified. When
> the "interface" argument is not specified, then interfaces with the
> literal name of * are searched and obviously, none are found. When I
> define the "interface" parameter like this:
>
> param $interface = *;
>
> ..then nothing is printed because $interface seems to be an empty
> node-set. As a next step, I tried with conditional statement:
>
> for-each ($result/physical-interface[name == (($interface) ? $interface :
> *)]) {
>
> }
>
> ..or:
>
> for-each ($result/physical-interface[name == (($interface != "") ?
> $interface : *)]) {
>
> }
>
> ..but those do not work either. On the other hand, "[name == *]" works
> fine.
>
> Am I doing it wrong or such statements are not supported?
>
>
> thanks,
> Martin
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