The Path to Homebrew

The home page and documentation for Homebrew show how to install and use Homebrew. However, they currently don't seem to explain exactly how pathing works. This can trip up a lot of newcomers, who might give up on Homebrew or fumble around the internet and land on bad advice - such as using sudo and editing /etc/paths. All of this is unnecessary and potentially dangerous.

You just really need to understand a few basic concepts:
  • Never run brew as sudo. Not "sudo brew install" nor "sudo brew link".
  • The "Cellar" is a place that all your "kegs" go. Homebrew installs packages to their own directory (in the Cellar) and then symlinks their files into /usr/local/.
  • Change /usr/local/* to be owned by $USER, not root, so you can have write permissions and not need sudo.
  • The $PATH entry for /usr/local/bin should occur before /usr/bin.
Here's an example of installing Python and setting paths correctly. I'm using OS X 10.9.2 (Mavericks) and Homebrew 0.9.5:
 $ sudo chown -R $USER /usr/local/*
 $ brew doctor
 $ brew update
 $ brew install python --with-brewed-openssl
 $ ls /usr/local/Cellar/python
 $ python
 >>> 2.7.5
Wait, I expected to see python 2.7.6 now. What happened?
 $ which python
But the Homebrew docs said we will be using a symlink from /usr/local/bin/ that points at the Cellar instead of using /usr/bin:
 $ ls -l /usr/local/bin/python
 lrwxr-xr-x 1 rkulla admin 33 Mar 2 06:37 /usr/local/bin/python ->
Aha. So it must be a PATH issue:
 $ echo PATH

 $ cat /etc/paths
When using Homebrew, we actually now want to change the position of /usr/local/bin to be before /usr/bin in $PATH. But don't edit /etc/paths. Instead edit ~/.bashrc and prepend /usr/local/bin to $PATH, like:
Next, run:
 $ source ~/.bashrc
 $ echo $PATH
 $ /usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin
Don't worry that there's duplicate entries for /usr/local/bin. It doesn't matter. What matters is that you've modified your PATH safely and ultimately cleaner than the other ways.
 $ ls -l $(which python)
 lrwxr-xr-x 1 rkulla admin 33 Mar 2 06:37 /usr/local/bin/python ->
Yay! And if you ever want to use the old python you can just run: /usr/bin/python.

Best of all from now on whenever you need to install anything with brew, you can just run:
 $ brew install whatever
and not have to fumble with permissions or worry about overwriting any global system files.

I also like to source ~/.bashrc from ~/.bash_profile. For why see: .bash_profile vs .bashrc
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