/usr/local question

[Jan Stary]

On Apr 04 23:32:26, Dominik Reichardt wrote:
> 
> On 04.04.2012, at 23:20, Jan Stary wrote:
> 
> > On Apr 04 16:05:27, Jeremy Lavergne wrote:
> >>> "/usr/local is not a viable choice because some software
> >>> (especially auto* tools from Gnu) look in /usr/local
> >>> as a default location, which means MacPorts can't be
> >>> easily isolated when needed."
> >>> 
> >>> I want to kindly ask the person who wrote this to elaborate,
> >>> and be as specific as can be: what exactly does it mean for macports
> >>> to be "isolated", and how exactly does e.g. auto* looking into
> >>> /usr/local stand in the way of it?
> >> 
> >> As with the software that magically found its way into /usr/local, how do we stop that very same software from clobbering what MacPorts has installed there?
> > 
> > You keep saying that: "the software that magically finds its way to
> > /usr/local". What do you even mean by that? The user installed it
> > there; that's about the only way something gets into /usr/local.
> > 
> > And how do we stop the user from rewriting something that is already there?
> > We don't, and we can't. It's the user's responsibility to not be an idiot
> > and rewrite something he has installed himself before.
> > 
> > In fact, what difference does "/usr/local or /opt/local"
> > (or any ther prefix for that matter) make in this respect?
> > In the current state of things, how do you stop the user
> > from overwriting something that macports has installed under
> > /opt/local?
> > 
> > You don't, because you can't. It's the user's responsibility
> > to not install over something that is already installed
> > (whatever the prefix is).
> 
> All kinds of software do actually install their stuff in /usr/local on OS X.
> Examples are a libpng framework from
> http://ethan.tira-thompson.com/Mac_OS_X_Ports.html

(1) Why would anyone use this when libpng is in macports?
(2) The site itself says "You will have the opportunity to select
[the destdir] during installation".

> or the Sane packages you get through following the links
> on the official sane site

(1) Why would you use this when sane is in macports?
(2) http://ljm.home.xs4all.nl/SANE-faq.html#35
	"SANE sits under /usr/local."

> (that's the two things that *magically* ended up in my /usr/local).

No it didn't magically ended up there. You installed it there.
And you were told before you installed it there that it will
end up there.

I see what you mean, but none of those is an example.

> The problem is that a couple of packages just install to /usr/local without explicitly stating that or giving the option to use another prefix. This is something you can't avoid and would mess up MacPorts if it were to use /usr/local.

That's right. With /opt/local you can't avoid it ether, can you?

> So in the above example this can mess up MacPorts builds when a port
> relies on libpng and wants the up to date libpng

When a port requires libpng, it says so in its Portfile;
and macports will install libpng (as present in macports,
not http://ethan.tira-thompson.com/Mac_OS_X_Ports.html)
as a dependency.