Where are the installation directories for homebrew?
brew installs binary in separate directories inside /usr/local dir. Then makes symlink inside /usr/local/bin. To get real path to binary type for example this (for tree command):

ls -l /usr/local/bin/ | grep tree


Output:

lrwxr-xr-x  1 slozo  admin    29 23 lip 15:06 tree -&gt; ../Cellar/tree/1.7.0/bin/tree


So my tree command is located in /usr/local/Cellar/tree/1.7.0/bin/tree