On MacOSX, if you have installed macports with the package installer, you may encounter the sudo: port: command not found problem.
Macports binaries are installed in /opt/local/bin, so you just need to add this path to your PATH environment variable. Example with your user, add to your $HOME/.profile :
You can source your profile file to update your environment:
$ source .profile
You are now able to use the port command:
$ sudo port -v selfupdate