[augeas-devel] Retrieving last modified node path (Was: First tests with aug mv)

[David Lutterkort]

On Sat, 2011-12-17 at 01:16 +0100, Raphaël Pinson wrote:
> 2011/12/17 David Lutterkort <lutter at redhat.com>
> >
> > On Sat, 2011-12-17 at 00:55 +0100, Raphaël Pinson wrote:
> > > 2011/12/17 David Lutterkort <lutter at redhat.com>
> > >
> > > > On Fri, 2011-12-16 at 14:01 +0100, Raphaël Pinson wrote:
> > > > > Resurrecting this old thread...
> > > > >
> > > > > We now have more calls that have the same issue as rm, namely setm and
> > > > > clearm, which modify more than one node.
> > > > >
> > > > > How could be adapt the idea to this? Maybe having several nodes under
> > > > > /augeas/tree/last_created and/or /augeas/tree/last_modified ?
> > > >
> > > > I would follow the model set by save and create entries
> > > > underneath /augeas/events,
> > > > e.g. /augeas/events/removed, /augeas/events/inserted etc.
> > > >
> > > > Right now, /augeas/events doesn't get cleared out in api_entry, but we
> > > > might consider doing that - or should we leave that to the user ? They
> > > > could then issue three 'rm' and just collect all the removed nodes.
> > > >
> > >
> > >
> > > If they get stacked in order, why not. aug_rm returns the number of nodes
> > > that were removed, so you know how many nodes you have to take out of the
> > > pile.
> > >
> > > So we could have something like:
> > >
> > > /augeas/events/removed[1]
> > > /augeas/events/inserted[1]
> > > /augeas/events/modified[1]
> > > /augeas/events/modified[2]
> > > /augeas/events/inserted[3]
> > > /augeas/events/removed[2]
> > > /augeas/events/removed[3]
> > >
> > > etc. where the last aug_rm call removed 2 nodes (and thus returned 2). You
> > > would then have to depile /augeas/events/removed[last()] and
> > > /augeas/events/removed[last()-1] to get their paths.
> > >
> > > Is that what you mean?
> >
> > After doing something like
> >  rm /foo/bar
> >  set /foo/bar 3
> >  ins bar before /foo/bar
> >  set /foo/bar[1] 2
> >
> > you'd have something like
> >
> >        /augeas/events/removed "/foo/bar"
> >        /augeas/events/created "/foo/bar"
> >        /augeas/events/inserted "/foo/bar[1]"
> >        /augeas/events/modified "/foo/bar[1]"
> >
> > How do you plan on using this info ?
> >
> 
> 
> Well, say you want to insert a node after a given node, and then use
> it. This is currently quite hard to do, but can be achieved with:
> 
> defvar mynode /files/path/to/file/somenode
> ins somelabel after $mynode
> defvar newnode /files/path/to/file/somelabel[preceding-sibling::*[1][$mynode]]
> set $newnode somevalue
> 
> 
> Using /augeas/events could make this clearer as you could do:
> 
> aug_insert(aug, "/files/path/to/file/somenode", "somelabel", "after");
> newnode = aug_get(aug, "/augeas/events/inserted[last()]");
> aug_set(aug, newnode, "somevalue");

Yes, definitely less of a head-scratcher; to make this doable in
augtool, we need a way to interpret the value of a node as a path
expression.

Maybe a function nodes in the path expression language so that you can
say

        ins somelabel after /files/path/to/file/somenode
        set nodes(/augeas/events/inserted[last()]) "somevalue"

IOW, nodes would be a function that takes a string (the value
of /augeas/events/inserted[last()]) and returns a nodeset.

David