AFAIK we have no choice in zsh but to tediously add things individually by hand to the various path environment variables. The Environment Modules System <https://en.wikipedia.org/wiki/Environment_Modules_(software)> for linux gives higher-level control, but it’s a whole ball of wax of its own. If I do this
	module load llvm/3.5.1
then the relevant directories from /usr/local/llvm/3.5.1 will be added to the front of PATH, LD_LIBRARY_PATH, LIBRARY_PATH, and CPATH, or whatever paths have been specified in the “modulefile” for llvm/3.5.1.

A zsh shell function could allow similarly convenient manipulation of paths, without buying into the whole Environment Modules thing.

Imagine a shell function called “paths”. Doing this:
	paths set /usr/local /usr /
wants to set PATH to this:
	/usr/local/bin
	/usr/local/sbin
	/usr/bin
	/usr/sbin
	/bin
	/sbin
and does so, except that directories that don’t exist, such as /usr/local/sbin, are not added.

An important convenience of the paths function would be that it also works similarly for MANPATH, LD_LIBRARY_PATH, LIBRARY_PATH, and CPATH.

You can also do these:
	paths remove /usr/local/llvm/3.5.1
	paths addlast /usr/local/llvm/3.5.1
	paths addfirst /usr/local/llvm/3.5.1
with the obvious effects (including removing from paths before adding at the desired position), and
	paths list
would output like this
	/usr/local/llvm/3.5.1
	/usr/local
	/usr
	/

One notable exception is adding “.” to PATH. The paths function could help here, too:
	paths --no-subdirs --only=PATH addlast .

On my Mac, here’s what’s in /etc/paths
	/usr/local/bin
	/usr/bin
	/bin
	/usr/sbin
	/sbin
But what about MANPATH, LD_LIBRARY_PATH, LIBRARY_PATH, and CPATH? The paths function could be smart enough to eat /etc/paths as input, stripping off the /bin part of each item and then doing:
	paths /usr/local /usr /
That way /etc/paths wouldn’t have to change. Better would be a new overriding file, called /etc/prefixes or something, that just has a list of arguments to the paths function:
	/usr/local
	/usr
	/

Comments? Volunteers? Is this already out there somewhere?

I do not plan to implement this anytime soon.

Dave