The discussion could go on for days on why I should be using virtualenv. On my Mac, I am not...much anyway. Get over it. Given this reality, I have a number of packages installed using the Python Package Index (pip) and want a command to keep them current. Digging around the interweb, there appears to be no built in way to accomplish this. Fortunately, there is somebody who knows a thing or 12 about the *nix command line and posted a great little snippet for accomplishing the task as a response on StackOverflow.
pip freeze --local | grep -v '^\-e' | cut -d = -f 1 | xargs pip install -U