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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 b…
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 b…
Right, that's what it's for, it's also why a 3rd party package manager shouldn't use it.