Homebrew - two newbie questions

[michellepace]

Hello, Before doing the below code I was wondering whether or not I was using the git installed via homebrew. I thought perhaps I was using another git on my system. I proved to myself that I wasn't:

mbp:~ m$ which git
/usr/local/bin/git
mbp:~ m$ brew list
git        ossp-uuid    postgresql    readline
mbp:~ m$ brew uninstall git
Uninstalling /usr/local/Cellar/git/1.7.5.4...
mbp:~ m$ brew list
ossp-uuid    postgresql    readline
mbp:~ m$ which git  can't find git anymore, so was using homebrew installed git
mbp:~ m$ brew install git
==> Downloading http://kernel.org/pub/software/scm/git/git-1.7.5.4.tar.bz2
...
==> Summary
/usr/local/Cellar/git/1.7.5.4: 1062 files, 19M, built in 15 seconds
mbp:~ m$ brew list
git        ossp-uuid    postgresql    readline
mbp:~ m$ which git  
/usr/local/bin/git  ....yay, homebrew installed git back again

Now looking at the code directly below I have two questions -

(Q1) How does my system know to use homebrew's "cellar" if I have no reference to the cellar in my $PATH?

(Q2) Why can't my system seem to find other stuff which is in the cellar? (eg postgresql)?

mbp:~ m$ brew --prefix
/usr/local
mbp:~ m$ brew --cellar
/usr/local/Cellar
mbp:~ m$ ls /usr/local/cellar
git        ossp-uuid  postgresql readline
mbp:~ m$ brew list
git        ossp-uuid    postgresql    readline
mbp:~ m$ echo $PATH
/Users/m/.rvm/gems/ruby-1.9.2-p180/bin:/Users/m/.rvm/gems/ruby-1.9.2-p180@global/bin:/Users/m/.rvm/rubies/ruby-1.9.2-p180/bin:/Users/m/.rvm/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin
mbp:~ m$ which postgresql    ??why can't i find these?
mbp:~ m$ which readline       ??
mbp:~ m$ which ossp-uuid     ??

thanks, Michelle