Is there a way to launch ScreenSharing from the Terminal?

Solution 1:

open vnc://server.address[:port]

Solution 2:

If you have access for assistive devices activated in System Preferences, you can try saving the following AppleScript in AppleScript Editor and executing it via command line:

tell application "Screen Sharing"
    activate # start Screen Sharing if not running yet
    tell application "System Events"
        keystroke "a" using command down # this will cause the address to clear
        keystroke "127.0.0.1" # replace with your host
        key code 36 # press enter
    end tell
end tell

Save as Sharing.scpt, and execute as osascript /path/to/Sharing.scpt.