On Sun, 2009-01-18 at 18:37 -0800, Robin Lee Powell wrote:
> Let's pretend that there was no alias type in Puppet (just because
> it's a file everyone's familiar with). Let's say that I wanted to
> set the postmaster alias to f...@bar.com using Augeas. The problem
> is, I have no idea what the Augeas path for postmaster is. The
> shell solution is something like:
>
> path=$(augtool match /files/etc/aliases/\*/name postmaster | sed
> 's;/[^/]*$;;')
>
> augtool set $path/value f...@bar.com
This is what I am trying to address with better path expressions in
Augeas itself. That lets you write
set "/files/etc/aliases/*[name = 'postmaster']/value"
f...@bar.com
to do exactly the same thing.
Path expressions are modeled on XPath, and the patches I have (and still
need to clean up some, but I've never been closer) implement a subset of
XPath that makes it possible to write down pretty powerful queries as
one expression
> I can't see any way to do anything like this in the Augeas type we
> have now, so I propose the following extensions, which would
> conflict with the "changes" argument. This would limit things to
> one change per Augeas type entry as far as I can tell, but oh well.
>
> command => set
> path => STRING
> value => STRING
>
> command => insert/ins
> where => before/after
> path => STRING
> value => STRING
>
> command => mv
> path => STRING
> destination => STRING
>
> command => rm/remove/delete
> path => STRING
>
> command => clear
> path => STRING
Isn't that just splitting the mini-language that changes currently
understands into attributes on the puppet level ?
> Nothing terribly exciting there; the new bit is that instead of
> "path" you can use one of these:
>
> match_path => STRING
> match_type => int/integer/size
> match_args => [ COMPARATOR, INT ]
>
> match_path => STRING
> match_type => regex/not_regex
> match_args => [ STRING ]
>
> match_path => STRING
> match_type => in/not_in
> match_args => [ STRING, STRING, ... ]
>
> The "size" and "in" types are basically identical to the current
> onlyif stuff. regex looks for a path that matches the given regex.
> not_in and not_regex match if the string isn't found or doesn't
> match the regex, respectively.
This mostly maps to 'predicates' in the path expressions; I don't have
support for regex matching in there yet, but other than that what you
describe above is covered.
This sort of brains (slicing and dicing the Augeas tree) really belongs
into Augeas - the Puppet type should mostly bridge the gap between
Augeas' command-oriented structure and Puppet's state-oriented veiw of
the world.
> Example 2
> ---------
>
> Again, working with the aliases file. I want to add an alias from
> "foo" to "b...@baz.com", but obviously I only want to add it once.
Again, expanded path expressions will help you here, since you can then
say
onlyif => "match /files/etc/aliases/*[name = 'foo'] size == 0"
David
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