Holger Parplies wrote at about 03:29:00 +0200 on Wednesday, July 20, 2011:
> Hi,
>
> sorry for not replying earlier. In case you're still wondering (otherwise for
> the archives) ...
>
> Jeffrey J. Kosowsky wrote on 2011-02-07 14:15:05 -0500 [[BackupPC-users]
> *BUMP* *BUMP* Re: BackupPC perl code hacking question... (Craig any chance
> you might have a suggestion?)]:
> > Let me rewrite my earlier posting to be more clear so maybe someone
> > can help me.
>
> Well, let's rearrange your message so it makes sense (did I ever mention that
> I don't like top posting? ;-).
>
> > > Jeffrey J. Kosowsky wrote at about 12:53:28 -0500 on Monday, December
> > 13, 2010:
> > > > For reasons I can explain later, I am trying to set
> > > > $Conf{RsyncdPasswd} in the main routine of BackupPC_dump (I am
> > > > actually trying to do something a bit more complex but this is easier
> > > > to understand).
> > > >
> > > > Now since %Conf = $bpc->Conf(),
>
> You are aware that this is a hash copy operation, right?
>
> > > > I would have thought that for example
> > > > setting $Conf{RsyncPasswd} = "mypasswd" would then be pushed down to
> > > > all the routines called directly or indirectly from BackupPC_dump.
>
> Well, it is as long as they use the "my %Conf" from BackupPC_dump and not
> $bpc->Conf(). You modified the copy, not the original hash in the
> BackupPC::Lib object.
>
> > > > However, in Rsync.pm where the value of $Conf{RsyncPasswd} is
> > actually
> > > > used, the value remains at ''.
>
> Yes, because Rsync.pm gets a reference to the unmodified BackupPC::Lib
> object's
> hash (BackupPC::Xfer::Protocol, line 59, sub new, "conf => $bpc->{Conf}").
>
> > > > (Of course setting the paramter the "normal" way within a config file
> > > > works and shows up as set in Rsync.pm)
>
> That is because the code in BackupPC::Lib that reads the config file saves
> the
> values.
>
> > > > I'm sure I must be missing something about how perl inherits and/or
> > > > overwrites variables... but I am stumped here...
>
> It's really simple. If you get a reference to a hash ($conf = \%conf), then
> you modify the original, if you get a copy (%conf = %conf_orig), you don't.
> What makes things complicated here is that you need to follow the code around
> through various modules and subs, and that each copy of %conf is named the
> same :-).
>
> > Here is a simplified version of my actual command
> >
> > $Conf{DumpPreUserCmd} = "&{sub {\$args[1]{RsyncdPasswd} = `ssh
> > -x mybackuypclient get_rsyncd_secret`}}";
> >
> > This uses the fact that $args[1]=$Conf
>
> Actually, it's \%Conf (a reference, not a copy), so modifying
> *BackupPC_dump's
> copy* works. $Conf would be a scalar, which might coincidentally contain a
> reference to a hash. Using an element of a hash is "$Conf{Foo}", using an
> element of a hash a scalar is pointing to is "$Conf->{Foo}". You might even
> have both visible at the same time, but only if you are either a bad
> programmer or enjoy confusing people.
>
> my $Conf = $bpc->Conf();
> my %Conf = (XferMethod => "snailmail");
> print $Conf{XferMethod}, "\n"; # probably prints "rsync"
> print $Conf->{XferMethod}, "\n"; # prints "snailmail"
>
> > So, that \$args[1]{RsyncdPasswd} is equivalent to
>
> ... a syntax error? ;-)
>
> $args [1] should be a reference to BackupPC_dump's %Conf, and
> $args [1] -> {RsyncdPasswd} should reference the corresponding entry (as an
> lvalue, so you can assign to it). "->" between braces "[]"/"{}" is implied
> and
> may be left out. I'm not sure how the reference operator binds in your
> example.
> As it seems to work, let's ignore it for now.
>
> > $Conf{RsyncdPasswd}.
>
> ... in BackupPC_dump (because that is what was passed in).
>
> > [...]
> > So, my question is is there any way to dynamically set Conf parameters
> > along the lines I am trying to do?
>
> Well, you'd have to modify the original hash.
>
> $bpc->{Conf}->{RsyncdPasswd} = `ssh ...`;
>
> That is not strictly legal, but it should work. Note that this change would
> *not* propagate to any copies previously made (like the "my %Conf" in
> BackupPC_dump). Using references to $bpc->{Conf} everywhere instead of copies
> would probably make things much easier, but on the downside, it would mean
> you
> can't make local modifications to $Conf->{...} that are not meant to
> propagate
> to the rest of the code (or, put differently, you could more easily
> accidentally clobber BackupPC::Lib's state). You'll notice that
> BackupPC::Xfer::Protocol (as quoted above) actually *does* use a reference.
>
> Hope that helps.
Hmmmm... very helpful...
Got it to work after correcting a pair of bugs in Lib.pm
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