[augeas-devel] Avoiding wheel reinvention with dpkg.cfg, and setting empty things.

[Robin Lee Powell]

On Wed, Dec 31, 2008 at 11:32:41AM +0100, Raphaël Pinson wrote:
> Hi Robin,
> 
> 
> Thank you for this nice lens. I see you've been putting quite a
> lot of info in comments in there. It would be nice if you could
> document using the standards described on [0], so your module can
> be included in [1].

Attached.

Also attached is my modifications to exports.aug for the same
purpose.

-Robin

-- 
They say:  "The first AIs will be built by the military as weapons."
And I'm thinking:  "Does it even occur to you to try for something
other than the default outcome?" -- http://shorl.com/tydruhedufogre
http://www.digitalkingdom.org/~rlpowell/ *** http://www.lojban.org/
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(*
Module: Dpkg
    Parses /etc/dpkg/dpkg.cfg

Author: Robin Lee Powell <rlpowell at digitalkingdom.org>

About: License
    This file, and the attendant test_dpgk.aug, are explicitely
    placed in the public domain.

About: Description
    dpkg.cfg is a simple list of options, the same ones as the
    command line options, with or without a value.

    The tree is a list of either comments or option/value pairs by
    name. Use "set" to set an option with a value, and "clear" for a
    bare option.
    
About: Usage Example

    $ augtool -n
    augtool> ls /files/etc/dpkg/dpkg.cfg
    #comment[1] = dpkg configuration file
    #comment[2] = This file can contain default options for dpkg.  All command-line
    #comment[3] = options are allowed.  Values can be specified by putting them after
    #comment[4] = the option, separated by whitespace and/or an `=' sign.
    #comment[5] = Do not enable debsig-verify by default; since the distribution is not using
    #comment[6] = embedded signatures, debsig-verify would reject all packages.
    no-debsig = (none)
    #comment[7] = Log status changes and actions to a file.
    log = /var/log/dpkg.log
    augtool> get /files/etc/dpkg/dpkg.cfg/no-debsig
    /files/etc/dpkg/dpkg.cfg/no-debsig (none)
    augtool> get /files/etc/dpkg/dpkg.cfg/log
    /files/etc/dpkg/dpkg.cfg/log = /var/log/dpkg.log
    augtool> clear /files/etc/dpkg/dpkg.cfg/testopt
    augtool> set /files/etc/dpkg/dpkg.cfg/testopt2 test
    augtool> save
    Saved 1 file(s)
    augtool>
    $ cat /etc/dpkg/dpkg.cfg.augnew
    # dpkg configuration file
    #
    # This file can contain default options for dpkg.  All command-line
    # options are allowed.  Values can be specified by putting them after
    # the option, separated by whitespace and/or an `=' sign.
    #
    
    # Do not enable debsig-verify by default; since the distribution is not using
    # embedded signatures, debsig-verify would reject all packages.
    no-debsig
    
    # Log status changes and actions to a file.
    log /var/log/dpkg.log
    testopt
    testopt2 test

*)

module Dpkg =
    autoload xfm

    let sep_tab = Util.del_ws_tab
    let sep_spc = Util.del_ws_spc
    let eol = del /[ \t]*\n/ "\n"

    let comment = Util.comment
    let empty   = Util.empty

    let word = /[^,# \n\t]+/
    let keyword = /[^,# \n\t\/]+/

    (* View: record
	Keyword, followed by optional whitespace and value, followed
	by EOL.

	The actual file specification doesn't require EOL, but the
	likelyhood of the file not having one is pretty slim, and
	this way things we add have EOL.
    *)

    let record = [ key keyword . (sep_spc . store word)? . eol ]

    (* View: lns
	Any number of empty lines, comments, and records.
    *)
    let lns = ( empty | comment | record ) *

    let xfm = transform lns (incl "/etc/dpkg/dpkg.cfg")
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(* Lens for Linux syntax of NFS exports(5) *)

(*
Module: Exports
    Parses /etc/exports

Author: Unknown

About: License
    Unknown

About: Description
    /etc/exports contains lines associating a directory with one or
    more hosts, and NFS options for each host.

About: Usage Example

    $ augtool
    augtool> ls /files/etc/exports/
    comment[1] = /etc/exports: the access control list for filesystems which may be exported
    comment[2] = to NFS clients.  See exports(5).
    comment[3] = sample /etc/exports file
    dir[1]/ = /
    dir[2]/ = /projects
    dir[3]/ = /usr
    dir[4]/ = /home/joe


    augtool> ls /files/etc/exports/dir[1]
    client[1]/ = master
    client[2]/ = trusty

    The corresponding line in the file is:

	/               master(rw) trusty(rw,no_root_squash)

    Digging further:

    augtool> ls /files/etc/exports/dir[1]/client[1]
    option = rw

    To add a new entry, you'd do something like this:

    augtool> set /files/etc/exports/dir[10000] /foo
    augtool> set /files/etc/exports/dir[last()]/client[1] weeble
    augtool> set /files/etc/exports/dir[last()]/client[1]/option[1] ro
    augtool> set /files/etc/exports/dir[last()]/client[1]/option[2] all_squash
    augtool> save
    Saved 1 file(s)

    Which creates the line:

    /foo weeble(ro,all_squash)

About: Limitations
    This lens cannot handle options without a host, as with the last
    example line in "man 5 exports":

	/pub            (ro,insecure,all_squash)

    In this case, though, you can just do:

	/pub            *(ro,insecure,all_squash)

    It also can't handle whitespace before the directory name.
*)

module Exports =
  autoload xfm

  let client_re = /[a-zA-Z0-9\-\.@\*\?\/]+/

  let eol = del /[ \t]*\n/ "\n"
  
  let option = [ label "option" . store /[^,)]+/ ]

  let client = [ label "client" . store client_re .
                    ( Util.del_str "(" . 
                        option .
                        ( Util.del_str "," . option ) * .
                      Util.del_str ")" )? ]

  let entry = [ label "dir" . store /\/[^ \t]*/ .
                Util.del_ws_spc .
                client . (Util.del_ws_spc . client)* . eol ]

  let lns = (Hosts.empty | Hosts.comment | entry)*

  let xfm = transform lns (incl "/etc/exports")