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 :

export PATH=$PATH:/opt/local/bin

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