cd to a directory by typing its name? For example if a directory 'blob' exists and I just type 'blob[return]' then the system cds into the blob directory for me.

In Linux (Ubuntu) I can add shopt -s autocd to my .bashrc file, but on OS X this gives an error: -bash: shopt: autocd: invalid shell option name
autocd was added in bash 4.0. You can install a newer version of bash with Homebrew and then change the default login shell with chsh:

brew install bash;echo /usr/local/bin/bash|sudo tee -a /etc/shells;chsh -s /usr/local/bin/bash


After you open a new login shell (or a tab by default in Terminal or iTerm 2), echo $BASH_VERSION should print something like 4.2.45(2)-release.

Terminal and iTerm 2 open new shells as login shells by default, so bash reads ~/.bash_profile but not ~/.bashrc. If you don't source ~/.bashrc from ~/.bash_profile or anything, add shopt -s autocd to ~/.bash_profile instead of ~/.bashrc.