Change keyboard layout to DVORAK from command line on Mac
This snippet did the trick for me. Note that I use Quicksilver to launch apps, so I remapped the keyboard shortcut for "switch input menu" from Cmd+Space to Option+Cmd+S.
osascript -e 'tell application "System Events"' \
-e 'keystroke "s" using {command down, option down}' \
-e 'end tell'