[augeas-devel] Why does Augeas fail to handle empty files?

Mol, Xavier (SCC) xavier.mol at kit.edu
Fri Feb 12 11:49:24 UTC 2016


Hi Raphaël.

 

> An empty file contains "\n", not "".

So what you are saying is, that Augeas doesn't understand the concept of empty files? It will always interpret them as beeing filled with an empty line (which translates into an empty tree node)?

 

Even though, that doesn't explain my question what the difference between

 

let lns = properties? . ( filler | domain )*

 

and

 

let lns = ( properties? . ( filler | domain )* )?

 

is.

 

Ciao,

Xavier.

 

 

 

From: Raphaël Pinson [mailto:raphael.pinson at camptocamp.com] 
Sent: Friday, February 12, 2016 11:00 AM
To: Mol, Xavier (SCC)
Cc: augeas-devel at redhat.com
Subject: Re: [augeas-devel] Why does Augeas fail to handle empty files?

 

 

 

On Fri, Feb 12, 2016 at 10:57 AM, Mol, Xavier (SCC) <xavier.mol at kit.edu> wrote:

Hi again.

 

> let lns = ( properties? . ( filler | domain )* )?

One more note on this: After I have changed this line, augparse compains that a very complicated regular expression "matches the empty word", which actually is the point of the exercise.

 

It shouldn't be. An empty file contains "\n", not "".

 

 

Raphaël

 

 

 

 

From: augeas-devel-bounces at redhat.com [mailto:augeas-devel-bounces at redhat.com] On Behalf Of Mol, Xavier (SCC)
Sent: Friday, February 12, 2016 9:13 AM
To: augeas-devel at redhat.com
Subject: [augeas-devel] Why does Augeas fail to handle empty files?

 

Hello Augeas experts,

 

this issue was mentioned in a previous mail thread on this list (see attached final mail) and I've run into it again: Augeas seems to be quite strict about empty files (as opposed to non-existing files).

 

I have a lens defined like this 'let lns = properties? . ( filler | domain )*'. The actual meaning of the sub-lenses is not important right now, since per regular expression this should successfully match the void. It indeed does create new files, but it fails to update empty files and this is the error message I get:

 

"""

[root ~]# >/etc/dcache/layouts/f01-151-109-e.conf

[root ~]# augtool

augtool> print /files/etc/dcache/layouts/f01-151-109-e.conf

/files/etc/dcache/layouts/f01-151-109-e.conf

augtool> set /files/etc/dcache/layouts/f01-151-109-e.conf/properties/dcache.java.memory.heap 2g

augtool> print /files/etc/dcache/layouts/f01-151-109-e.conf

/files/etc/dcache/layouts/f01-151-109-e.conf

/files/etc/dcache/layouts/f01-151-109-e.conf/properties

/files/etc/dcache/layouts/f01-151-109-e.conf/properties/dcache.java.memory.heap = "2g"

augtool> save

error: Failed to execute command

saving failed (run 'errors' for details)

augtool> errors

Error in /etc/dcache/layouts/f01-151-109-e.conf (put_failed)

  Failed to match

        { /properties/ }?

(    { /#comment/ = /[^\001-\004\t\n\r ][^\001-\004\n]*[^\001-\004\t\n\r ]|[^\001-\004\t\n\r ]/ }

      | { }

      | { /domain/ = /[$.0-9A-Z_a-{}-]+/ })*

  with tree

    {  } { "properties" }

  Lens: /var/lib/puppet/lib/augeas/lenses/dcachelayout.aug:29.12-.46:

"""

 

For some reason, there is an empty node before the properties node, which failes the put direction. For that the lens needs to be written like…

 

let lns = ( properties? . ( filler | domain )* )?

 

As far as regular expressions go, there is no effective change here, right? Yet for Augeas this clearly seems to make a difference. Can someone maybe explain this to me?

 

Thank you for your time,

Xavier.

 

 

****

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 <tel:%2B49%20721%20608%2023041> 

Email:  <mailto:xavier.mol at kit.edu> xavier.mol at kit.edu

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****

 

 


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