[augeas-devel] How to select nodes in distinct position, possibly creating them?

[Mol, Xavier (SCC)]

Hello Augeas experts,

I'm looking for a way to select a node in an Augeas tree in a distinct position, which isn't difficult, but I also want to create that node in case it doesn't exist yet, which seems impossible to me as of now. An example probably illustrates better what I mean...

augtool> touch /t/#comment
augtool> ins "" after /t/*[last()]
augtool> touch /t/B
augtool> touch /t/C
augtool> print /t
/t
/t/#comment
/t/
/t/B
/t/C


What can I do now to make a node "A" appear right in front of "B"? The straight forward answer is, like this:

insert "A" before "B"

That works fine as long as there is no "A" node already, which I can't know beforehand. I could guarantee that there is no such node, by deleting it first (this very trick was taken from the Augeas wiki: https://github.com/hercules-team/augeas/wiki/Path-expressions#Tips_amp_Tricks).

augtool> rm /t/A[following-sibling::*[1][self::B]]
rm : /t/A[following-sibling::*[1][self::B]] 0


However, this way I might destroy any children of "A", which henceforth are lost. In other words, I'd replace "A" instead of updating it.


Normally one selects specific nodes with 'defnode', which will create new nodes if no match was found.

augtool> defnode newNode /t/A[following-sibling::*[1][self::B]]
augtool> print /t
/t
/t/#comment
/t/
/t/B
/t/C
/t/A

The problem this time is, that the new node will be appended to tree in last position, so it needs to be moved to the correct position manually. And 'mv' in turn has the inherent drawback, that it cannot target relative positions, only specific destinations. Which means, replacing existing nodes, which I don't want.

Does someone maybe have a solution to this? Or is this another situation that needs to be dealt with by applications utilizting Augeas, since Augeas doesn't interpret the format of the files it edits?

Thank you for your time,
Xavier.

PS: I'll be on holidays next week, so I won't be able to answer any replies until I've returned.


****
Karlsruher Institute of Technology (KIT)
Steinbuch Centre for Computing (SCC)

B. Sc. Xavier Mol
GridKa Storage Administrator and Support Manager

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Phone: +49 721 608 23041
Email: xavier.mol at kit.edu
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