Les Mikesell wrote:
> > thank God you're sensible about this, Craig. Entirely too many perl
mongers
> > have the idea that just because one can put perl script into a config
file,
> > that it should be done. (Witness the abominable config files for
LogWatch).
>
> I have to disagree on this one, although in a pure-perl app it
> doesn't matter a lot and with a cgi interface you need to know
> what executes every hit and what doesn't. MimeDefang is a great
> example of where the config file being a snippet of perl allows
> the local admin to easily do things no one else had even considered,
> something that's impossible if all you can do is set some canned
> variables.
I'm of two minds myself about this.
First, it's not just that one can add Perl code to the config file,
it's that it _is_ Perl code already. And that makes for interesting
features that are not possible
in regular config files, like nested data structures. Take for example
something like
$Conf{BlackoutPeriods} = [
{
hourBegin => 23,
hourEnd => 3,
weekDays => [1, 2, 3, 4, 5, 6, 7],
},
];
That is a concise, readable (at least for me), and flexible way to express
blackout periods. With
a normal config file, it would be possible to express that, of course, but
it would be much more clumsy.
Then, the possibility of going beyond the mere assignment of variables
gives one
extra flexibility when needed. Of course, in that case you need to know
Perl.
As an aside, there is an even more readable format for config files, YAML
(http://www.yaml.org), which is really not just for that, but is intended
to represent any data structures in a language-independent way. I love it
and use it all the time, but it still is limited to data, not code (and I
would like it to stay that way).
Second, the fact one can add code to a config file doesn't mean I'm for
littering it
to the point of making it an unreadable monster. There should be some
restrain on what one adds to such a config file. For instance, if a
solution to a problem, implemented
this way, proves to work and is sufficiently popular, then it may be time
to consider it
for inclusion in the main code. So then, the possibility of
experimentation, which is
why I've done it that way, is an important reason to have a Perl-code
config file.
> > Other reasons to avoid scripts in config files:
> > a. it makes the config confusing to read, even for those people who can
> > write perl
Out of the box, as originally distributed, config files probably shouldn't
go beyond assigning variables statically, I'd agree with that. But why
unnecessarily limit the extent of customizations that can be done after
installation?
> It doesn't have to be confusing. I'd rephrase your comment above
> and say that just because it can be confusing doesn't mean it
> should be.
>
> > b. it's immediately discouraging to those of us who can't
>
> Learning perl will save time for a system administrator. But
> you should only need to know it to do things that would otherwise
> not be possible at all.
>
I completely agree here. There are always going to be special needs that no
generic setup can acommodate. Knowing how to program in Perl (Perl's my
favorite language, but other dynamic languages may often be just as good
for a particular problem), will "make easy thing easy, and hard things
possible", as one of Perl's mottos goes. And having the config file be Perl
makes the solution one step closer to the BackupPC code than it would be
otherwise.
Bernardo
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