Because /usr/local doesn't belong to homebrew and is not appropriate for homebrew to commandeer.
MacPorts was originally written by the BSD team at Apple; if /usr/local was where a packaging system was supposed to stuff itself on OS X, they would have used it -- instead of /opt/local.
The co-opting of /use/local breaks all kinds of stuff -- for instance, /usr/local/lib is in the default linker search path and can't be removed, which means that trying to not link against homebrew libraries requires some pretty evil hacks -- such as library symbol interposing to hide /usr/local from stat(), etc.
I disagree. / is where the stuff needed for single-user mode gets installed. /usr is where the OS's userland stuff gets installed. On Linux systems this includes everything that you get from your package manager, because this is considered to be part of your system. /usr/local is wher you install your own packages. For example, if I'm installing something from source, that's where I'm going to install it. Or if I'm building my own project, I would also install it there.
On a Mac, there is no system-blessed pacakage manager - the official packages are pre-installed on your Mac and only change when you get an OS update. They tend to be installed in /Library or ~/Library. All of the add-on package managers therefore play a role much closer to that of hand-installed source. It's logical that they install to /ur/local. In particular, one of my main use case for package managers is when I want to try out a package that has a whole bunch of dependencies. I might want to compile the package that interests me by hand, as I need to tweak the config, but I don't want to have to do the configure-make-make install dance for the 30 packages that it has as dependencies. That's where homebrew / MacPorts comes into the picture, they save me that work. But they should be installed into the same hierachy as the package that does interest me, as they are at the same level of "officialness".
One last thing. I know Fedora, Gentoo and MacOSX fairly well, and I have also worked a fair bit on a hand-rolled linux distribution. None of them ever had /usr/local/lib in their LD_LIBRARY_PATH by default, I've always had to configure that in my .bash_profile. This is exactly what you would expect, by default the directory should be empty, so why add it to the default LD_LIBRARY_PATH, that doesn't make any sense.
> On a Mac, there is no system-blessed pacakage manager ...
Which is one very big reason why commandeering /usr/local for a single package manager is inappropriate; it means that your 3rd-party package manager cannot share the system with any other 3rd-party package manager.
To re-iterate -- the BSD team, who maintained hier(7), very intentionally didn't put MacPorts in /usr/local.
Well, it usually installs from source, but that's not really the point. It's a package manager, it is trivial to give it it's own home, (and thankfully they made that an easy thing to do), but to throw it in that /usr/local bucket by default? It seems like a decision that requires real justification and the reasons I have seen seem pretty weak.
I mean, in the end it seems like almost nobody cares, but it's always been a pet peeve of mine.
I get what you're saying, but /usr/local is where I install stuff. I'm happy with having the thing that does little more than untangle my dependencies before running `make` for me with sane defaults use it too.
I expect to find system-specific applications in /usr/local. I get the argument otherwise, and it has merit, but not enough to not do it, if you get me.
Can I ask what you use your package manager for? My experience on the Mac is that it's mostly used by developers that want to install a package and don't want to have to manually install the 30 other dependencies by hand. For that use case, installing the dependencies along side the module that you actually wanted seems like an eminently reasonable thing to do, and certainly in my case it's pretty much exactly what I want from a package manager on the Mac. I assume if it bugs you that you have a different use case from mine. I would be interested to hear what it is (have I been missing opportunities on my Mac all this time???)
