how to uninstall emacs from command line?
emacs is actually a virtual package, provided by emacs23-lucid or emacs23-nox. It's these that should be removed:
sudo apt-get remove --auto-remove emacs23-lucid emacs23-nox
The --auto-remove removes any packages which were installed to fill a dependency, but are no longer needed. In this case, it will remove packages like emacs23-bin-common.