Apple - Start/stop internet sharing from a script?

To start Internet Sharing from the CLI:

sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.InternetSharing.plist

To stop, change the load to unload.

Note that if you have the pref pane open when you run this you will not see the change take effect immediately (the UI won't update), but it does work.

One way of doing this is by GUI scripting—System Preferences doesn't have any Applescript support by default.

tell application "System Preferences" to set current pane to pane "com.apple.preferences.sharing"
delay 1
tell application "System Events" to tell process "System Preferences"
    click checkbox 1 of row 8 of table 1 of scroll area 1 of group 1 of window "Sharing" -- change to row 10 if you are using anything before Snow Leopard
    delay 1
    if (exists sheet 1 of window "Sharing") then
        click button "Start" of sheet 1 of window "Sharing"
    end if
end tell
ignoring application responses
    tell application "System Preferences" to quit
end ignoring

I had far better results (for an already configured sharing setup) on 10.11.6 with the simple variations...

sudo launchctl start com.apple.NetworkSharing

and

sudo launchctl stop com.apple.NetworkSharing

respectively.